Third Secretlab, it’s still pricy but far more affordable than HM, has all the lumbar support, and whilst it looks gamer-y it lacks the awful shoulders that makes it bad for you so it’s actually comfortable.
I had to WFH at my parents for 1 day the other week, couldn’t believe how bad my back pain got from 1 day in a crappy office chair. Their support was good too, my magnet head rest kept falling down so they sent me a brand new one
Sports but not specifically walking, I use FitNotes. I mostly use it to track my weightlifting progress but it does have the ability to track time so I do track my cardio on the same app.
It has Google Drive backups too which is nice