While I decide whether to buy a treadmill or not, I do my "walks" inside my home.
Whenever I cannot walk outside, I place a high-back chair fronting
the TV, drop a plastic (not rubber) mat on the floor behind it, put my hands at
each end of the top of the chair to keep balance (not really necessary) and stand on the mat to begin
"walking" as I would in any treadmill, maintaining the speed I can tolerate.
The mat will allow the feet to slide as necessary and I can start/stop the
exercise at will. I measure my progress either by counting the minutes or the
number of (leg) strides. I also do the "walk" by bending the knees as if I were
marching. I find this a terrific stationary walk when other means are not
possible. The above is provided not as an advice but only to share my
experience. For those with health or other issues , please consult your doctor
before trying this exercise. PS. I ride a bike but that depends on the weather.