Participants will receive generic health advice only and it will not be individually tailored, nor will they receive weekly support phone calls during the first 12-weeks. Participants will receive no feedback or support in the Maintenance or Follow-Up phases.

The intervention feasibility will be measured by Holden's Simplified System Usability Scale questionnaire, participant reported. The Holden's Simplified System Usability Scale is 10-item design, five-item agreement-based Likert scale, from Strongly agree (5) to Strongly disagree (1) with total scores ranging from 10- 50. It allows you to evaluate software, mobile devices, websites and applications. A higher score indicates greater usability.

The intervention acceptability will be measured by the Health Care Climate Questionnaire (participant reported). This is a 6 item (shortened version) using a 7-point Likert-type scale, from Not At All True (1) to Very True (7). The total scores will range from 6 - 42 and a higher score indicates greater acceptability. The preamble and wording of each item will be altered, to better align with the Small Steps intervention and the role of the health professional.

The intervention acceptability feasibility will be measured by a Behavioural automaticity (Self-Report Behaviour Automaticity Index) questionnaire. Participants rate items (such as "Physical activity is something I do automatically") on a scale ranging from 1 (strongly disagree) to 7 (strongly agree). Participants will complete the measure in relation to four different behaviours; physical activity, sedentary behaviour, and good sleep practices with each of these 4 behaviours ranging in scores from 4-28. A higher score indicates greater automaticity for that behaviour.

The intervention feasibility will be measured by self-efficacy and intention questionnaire (participant reported). Participants self-efficacy for physical activity will be captured through the self-efficacy for exercise scale. Intention to be physically active and perform positive sleep behaviours will each be assessed. Participants will respond on a 7-point Likert scale with options ranging from 1 (Strongly Disagree) to 7 (Strongly Agree). The total scores will range from 7- 14, with a higher score indicating greater feasibility of the intervention.

Participants' satisfaction of their psychological needs of competence will be assessed using the Perceived Competence Scale. This is a short 4-item questionnaire assessing participants' perceived competence to exercise. Participants respond to the 4-items using a 7-point Likert type scale, ranging from 1 (not at all true) to 7 (very true). The total scores will range from 4 - 28, with a higher score indicating greater participant confidence and feelings of competence.

A single Semi-structured exit interview will elicit rich data on participant experiences, perceived burden, suggestions for improvement and barriers to feasibility.

Continuous recording using a wrist-worn activity monitor (FitBit) with daily time-use derived from a 7-day average. Time spent in sedentary, light, moderate-to-vigorous and vigorous physical activity (min/day).

Self-reported sleep quality as measured by Pittsburgh Sleep Quality Index (PSQI). The PSQI is 19-item self-report index to assess sleep quality. The questionnaire consists of a combination of Likert type and open-ended questions (later converted to scaled scores using provided guidelines). Scoring provides an overall score ranging from 0 to 21, where lower scores denote a healthier sleep quality.

Self-reported sleep quality as measured by Sleep Hygiene Index (SHI). The SHI is a 13-item self-report index designed from the ICSD to assess the presence of sleep hygiene behaviours. Each of the item is rated on a five-point Likert scale (ranging from 0 [never] to 4 [always]). The total scores ranged from 0 to 52, with higher scores indicating poorer sleep hygiene status.

Continuous recording using a wrist-worn activity monitor (FitBit) with daily time-use derived from a 7-day average with sleep time measured in minutes per day.

Score for Trail Making Test. The Trail Making Test (TMT) is a timed neuropsychological test that involves visual scanning and working memory. The TMT is scored by how long it takes to complete the test (seconds). Norms have been established based on age and education and the lower the number of seconds taken the better the cognitive functioning.

Score for Digit Span Test. This test measures short-term verbal memory. The total number of lists reported correctly is combined across forward span (FS) and backward span (BS) to produce a total correct score. Outcome measures include the direction of the task (forwards or backwards), the longest sequence successfully reached and passed, and the total number of attempts. The higher the score the better the cognitive functioning.

24-hour time use will be captured via self-report using the Multimedia Activity Recall for Children and Adults (MARCA) tool (30). The MARCA will be conducted via telephone call with a trained researcher and requires participants to recall every activity that they engaged in over the past two days from midnight to midnight, in minimum 5-minute increments. The MARCA tool contains over 500 activities linked to an activity compendium, allowing 24-hour time use to be conceptualised in terms of both activity types and activity intensities (through linking each individual activity with its metabolic equivalent per the compendium).

Participants' motivation to be physically active will be captured using the Treatment Self-Regulation Questionnaire. Participants will respond to 15 questions relating to reasons for beginning or keeping regular disease self-management, such as "Because I personally think it is best for my health" and "Because I would feel guilty or ashamed if I did not manage my own disease" using a 7-point Likert-type scale (1=not true at all, 7=completely true).