If you are buying your first piece: a wedge, not a ramp set. It is the cheapest way to find out whether you will actually use one, it stores under a bed, and it solves the most common problem people come here with.
If the reason is pain or access: buy on shape and firmness, not on the brand. A wedge supporting a hip or a lower back is doing a physical therapist's job, and firm does it better than plush.
If you want a swing and you rent: door mounted. It hangs off a closed door and leaves no holes. Ceiling mounted swings need a joist, and they are not coming down before you move out.
If it has to live in a bedroom other people see: check the shape before the price. A wedge in a neutral cover reads as a cushion. A stool or a pole does not, and no amount of upholstery changes that.
On cleaning: removable washable cover, every time. It is the one spec that decides how long a piece lasts, and a waterproof throw underneath saves the furniture and the mattress both.
If you are planning a whole room rather than one piece: our guide to building a sex room covers what goes in, what to skip, and what people end up regretting.