The Prone Tiger
From behind with the receiving partner lying face down over the seated partner's outstretched legs.
The giving partner sits upright on the bed with their legs stretched out straight in front of them. The receiving partner lies face down across the giving partner's legs, facing away, with their hips settled in the giving partner's lap and their chest and arms resting on the bed beyond the giving partner's feet. The receiving partner's own legs stretch back behind them, one on either side of the giving partner's hips. The giving partner keeps their back straight, holds the receiving partner's hips or lower back, and moves with a slow rocking of the pelvis. A pillow under the receiving partner's chest makes the lie more comfortable, and sliding the hips a little higher up the lap changes the angle.
Depth from behind with the receiving partner almost completely at rest, and the giving partner's hands free to stroke their back.
The giving partner can sit against the headboard so they don't have to hold themselves upright.
The receiving partner can rock back toward the lap to set the depth. Agree beforehand who leads.
Deep positions can hit the cervix or press on tender spots. Start shallow, let the receiving partner set the depth, and ease off at the first wince.
Agree on it before you try it, use plenty of lube, and either of you can stop at any point. This guide is general information, not medical advice.