@luvcats mentioned in her knee thread the challenges of sitting in a chair with recovering knees, and also, the need to walk in the night.
I found sitting up in a chair with legs at a 90 degree bend (or really any at first) difficult for a long time. My OS suggested easing the affected leg out in front a bit, and very slightly resting/elevating the foot/feet in your case? on something. Sort of like the place in the floor of the car where you can rest the foot? I used a pillow, a yoga block, my birding encyclopedia, rolled up towels, etcetera, at varying times. At present, the 2-pound squishy ball that was originally for shoulder exercises (years ago, before the tear) is kept under the great room coffee table and gets rolled out for whichever foot/knee needs a little lift. I do under the foot rolls on it before pushing it back under the table (I have 2 foot threads).
Our eat-in kitchen table is counter height with very high, but very comfortable padded chairs. Great for doing that leg swinging exercise. I had to add a footrest, as the bend to the rest bar on the chair was too much. I ended up with a smallish (6 inches high maybe?) rectangular storage tub with a folded towel on it. Not tres chic decor, but made the knee(s) happy. Actually, it is still there, but with a towel that goes better with the travertine.
Lastly, during both knees early recoveries, I found the little night walks very helpful. Noticeably less stiff the following morning.
I get up once most nights now to walk to the bathroom. My challenge is to walk enough to relieve stiffness (mostly now), particularly before bending the knees for the commode (18”—I have finally removed the even higher over the commode seat and rails and legs that I needed for the sprained ligament) and/or pain without waking up so much that I have trouble going back to sleep. I use APAP for mild sleep apnea. Ideally, there and back is enough (40+ steps roundtrip). If I add walking, I do it in the bedroom first. So when I head back, it is to lie down and sleep.