I often lay down to meditate, but I want to switch to sitting. How do you sit and meditate? In a chair? On the floor?

I sit on the bed or the floor, with a pillow on the right spot to feel relaxed. I just sit on the edge of the pillow, for the pelvis to ”tip up”

Basically sit anywhere comfortable. On the bed or on the floor is better. The great meditators like Buddha has meditated while sitting. I find it very comfortable while meditating sitting. If your legs get sore switch your posture.