Prolapsed womb

Tbh I think the best person to advise you is your clinician, because presumably they know how bad it is and what is possible.

The heavy lifting advice is correct. I have had a prolapse for seven years now and until the last 18 months I have found a ring pessary kept the prolapse in check and I was able to walk as far as I wanted without a problem. Have you been offered a ring pessary fitting? If it stays in place you won’t feel the pessary or the prolapse, it just has to be changed every six months.

If you feel comfortable walking, then it's good exercise.

I had surgery for prolapse. I didn't think that walking affected the prolapse. Some exercises are bad for prolapse. There's an Australian women's health physio called Michelle Kenway who has a website and gives appropriate exercise and activities. Heavy lifting does make it worse and should be avoided post surgery as well.
Once things are back to normal, it is worth asking your GP to refer you to a Urogynaecologist for advice on whether a pessary, surgery or some other treatment is best for you.