Walking and cycling are particularly good. You can do them right from your front door, and include them as part of your daily routine. Walk the kids to school. Cycle to the store or to work. Others are more complicated and costly.
Some activities are naturally more gentle than others.
Cycling and swimming both support body weight. Walking is great, too. You can start at a leisurely pace and build up gradually. Other activities are more demanding, but with proper care and attention, injuries needn't be a problem. Running requires good shoes, for example.