One easy sex position that allows for a lot of penetration is the Pancake with a Pillow.
For individuals who experience back pain, it can be helpful to add a cushion or sex furniture under the head or lower back to enhance the comfort in this posture.
A pillow or towel placed under the lower back of the receptive partner helps them get into this sex position. Kneeling down, they draw their legs up to their armpits. When one person leans forward for more physical contact, kissing, or snuggling, or when one kneels upright, there's plenty of space for the penetrative partner to play with the receptive partner's clitoris or penis.
Further Information about Pancakes While Seated on a Pillow
If you're looking to spice up your wrist bondage routine, try swapping out the cushion for some Liberator sex furniture, like the Black Label Wedge.