My cats tend to sleep where they want...usually the cat tree, a recliner, or snuggled up with one of us. They do have three cat beds scattered about the apartment (used to be four before Rochelle used it as a litter box :?), all are different types...one is round with sides, one is rectangle and side-less (like a small dog bed), and one is a plush enclosed box. Samantha is my only girl who uses them, and she uses them quite frequently. Rochelle will get in the box on a rare occasion, and I don't think I've ever seen Alice even touch a paw on one. They were all cheap though (most expensive one was $9.99), and if Samantha likes them, then she gets them. She likes to follow me from room to room and no matter where I settle, there's a cat bed waiting for her to sleep right next to me.
As for suggestions, I'm with Susan and say go with something similar, if they are both wanting the one you currently have. Maybe make a subtle change...try one without sides if your current one has them?