The Star
The receiving partner lies back with one knee up; the other partner kneels astride their straight leg and leans back on their hands.
The receiving partner lies on their back, relaxed, with one leg stretched straight out and the other knee bent, foot flat on the bed. The other partner kneels astride the straight leg, facing them, with their own legs either side of it, and slides close. Once connected, they lean back and plant their hands on the bed behind them so their hips tilt forward. The receiving partner can rest their hands behind their head and simply enjoy it, or hold the raised knee out to the side to open up. Letting the bent knee fall outward changes the angle; bringing it in across the other partner's waist makes things closer.
A lazy, open position for the receiving partner, with a slightly sideways angle that's different from missionary.
The kneeling partner can stay upright with hands on the receiving partner's raised knee instead of leaning back.
Switch which leg is raised halfway through. It's a small change that feels new.
Hard floors are rough on knees. A folded towel, pillow or thick rug underneath makes a real difference.
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.