There were quite a few of these threads several years ago, One community member was working on a VA project which included inhome wellness monitoring for people with traumatic brain injury. The ultimate conclusion was that smartthings just wasn’t reliable enough for this for critical use cases, but it could be helpful as an additional convenience notification.
Although a lot of the code and some of the devices will be out of date, it might help give you some ideas although the implementation details will differ. You can check at two different tags: project alerts, and project accessibility, to find these.
https://community.smartthings.com/tag/project_alerts
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https://community.smartthings.com/tag/project_accessible
As far as the specific issue of getting out of bed, the quickest would be either a pressure mat under the mattress or a motion sensor or both.
The Withings sleep monitor costs about $80 and has an IFTTT channel, so you can get the whole thing up and working in about 10 minutes.
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So that would probably be the easiest. But there are other options as well.