Had a fwb who loved to do this before I met my wife. All I had to do was lift up and she would dive in. Also was at a swing club on a multiple men night for women and a wife (whose clothed husband only watched as his wife was pleased with many men) came over to me when I was jerking off sitting down and threw my legs I. The air to dive in. I was in heaven. Sadly my wife only did this once after showering together. I’ve asked but she said it was a one time thing. 