I swim!
Backstory: in my late 30's I started running (again), and decided to run half marathons. Did two, plus a few other long races, got injured (piroformis), cut back my distance, took up triathlons (but sprint ones), went through physical therapy.
Still had the issue with piriformis and sciatica, quit running. Started up again the following year to train for the tri again, except using Vibrams. Fixed the piriformis! But gave my achilles tendonitis.
Anyway, stopped running again. At that point I started doing swimming and spin classes. Early morning is really the only time I can work out, at 5:30 am. So I go to the pool 2x a week at 5:30 am. I feel like I:
1. Get a good workout, though I'm slow
2. It's not hard on my body, though I have to be careful of my left shoulder
3. I can lose myself in my thoughts, hard to do with a FT job and 2 kids. (I swam all through 2nd pregnancy).
I love it. It's awesome.