I play sitting down, and I do two things to make myself more comfortable:

I put my right foot on something about 3 -4 inches thick.

I put a soft pad on the front edge of the guitar to keep it from digging into the flesh above my elbow and stopping circulation there.

Here are some other observations:

Some people press the little finger of their picking hand on the top of the guitar. Why!? It feels awful and locks your hand up.

Using a pick for a long time is bad for your hand. Switch to fingerpicking or give yourself a rest.

I have seen guitarists whang away at high speed for an hour at a time (say with a high-energy Irish band.) Surely they are asking for a case of tennis elbow.

After you do a song, stand up, flex your arms, move around a bit. Don't stay in one position for a long time. Human beings evolved to be in constant, slow motion. That is why there is no such thing as a perfect chair or mattress.