You can do assisted squats. here are three ways
1) Hang onto a door knob (the opposite side of the door to the way it opens so it doesn't pop open on you) lean back a bit and drop into a squat as far as you are comfortable - use your arms as somewhat of an assist.
2) open a door and hang a long towel over the top. Grab an end in each hand facing the door. Do a squat with your knees to each side of the door - again use your arms to assist and only drop down a comfortable amount. You can adjust your foot placement wider/naroower - closer or fartehr from the door. If the towl slip[s off you will land on your ass. You can also hang onto the door knob on either side of the door as well. You will progress
3) put a chin up bar in an un-used doorway at about nipple/shoulder height. Hand onto it like you were doing a chin-up. The drop into a squat use your arms to assist you. Try standing farther away or closer to the bar to get different effects. Use an under hand or overhand grip as you like. You can buid arm strength too as you use your arms to lift yourself. You can use this to do really fast 'chin-squats' and do Tabata style intervals once you get quiker and stronger.
OR You can do step ups. - with or with out weight. Uas a small step say 10 to 12 inches to start - if too strenuous go to lower step. Yes you can use your stairs. You can also curl a hand weight or do shoulder presses while stepping.
You can also step up with some very heavy weights if you like.
I like to use a box that I can straddle. I stand on the top of the box. I step off to the left with my left foot then back up on the box and off to the right with my right foot I can do this slowly with heavy weights or I can use a lighter weight and go very quickly to do intervals.
Hope it helps - remember - go slow - progress will come.
OR You can also do chair squats. Just squat down onto a chair seat and then back up. As you get better and can do more- use a lower chair. Or if you can an exercise ball you can drop your but down onto the exercise ball and use it to bounce your way back up - sort of an assisted quat. I would place the ball in a corner so it can move the first few times you try this.