if those things are easy for you, find progressions for each movement to make them harder.

I'm using this guy's pushup progression because I want to do one-handed ones

I usually aim to do 3 sets of 6 pushups and then move to the next one, going to failure on the new version then going until tired on the old version (still 3 sets of 6+ pushups of some variety).

AthleanX on youtube has a lot of gimmicky videos, but if you have a specific workout you want a progression on they have good stuff too.

Make sure you get your leg muscle stretches in! It's not a workout but I have a messed up knee too and it's only ever gotten better and stayed better after stretching for extended periods of time.

Russian twists!

Yoga! (<-- very important to prevent cramps)

Planks!

Chair dips!

Leg lifts!

Crunches and Reverse Crunches!

A lot of these are core, but core strength adds to every other strength so you should train it every time.

I’m definitely not an expert, but here are some of the low/no equipment exercises I do with my trainer:

• Hip bridges, you can also just put something heavy on your stomach if it’s too easy with just your body weight
• Mountain climbers. You can do this on the floor or something around bench/couch height if you need to modify.
• We do a ton of variations of step ups/step downs, you would need something stable to step onto. Doesn’t have to be very high but you might need to hold weight if you feel you’re not being challenged.
• Planks
• Wall sits
• There’s also lots of ways to modify squats like sumo squats, one-legged squats and probably a lot more.

I don’t do these, but you could also do burpees or jumping jacks.

50 burgers/50 situps. Then 40/40, 30/30, 20/20, 10/10.

You can adjust the intensity based on how you're feeling.