This may be the simplest “hack”, but it’s also one I wish more students used. Something as rudimentary as a bandage can work wonders to draw the physical attention (that is, the body’s awareness of what is happening while other complicated things are going on) to a small, but crucial aspect of technique.
I use this approach on either hand, and it’s up to you whether you splint the thumb so you only start feeling a squeeze when your technique starts to falter, or you set the tension such that it feels a little more sensation when you’re in the right posture, and the feeling fades as your technique moves further away from the ideal.
It likely depends on whether your thumb curves and jams or hyperextends and slips.
The main thing to remember, throughout all your practice, is that the cello is a mostly physical pursuit. You should be monitoring and making changes to physical phenomena, and to the inner processes (stresses, trying to play too quickly, not having clear ideas) that affect them. The answer is almost always to be slow, deliberate, with clear physical goals and a way to judge whether you have accomplished them or not.