When choosing a trapeze bar, you should consider the following things: your activity, your weight, and the space that you have available in the room.
If you want to have a multiple-use trapeze bar, you should buy one that is free-standing. You can move it anywhere in the room so that you can use it to help you with getting up, with the transfer on your wheelchair, as well as with the physical therapy.
However, if you don’t have enough space and your needs are not that special, you can buy a bed or ceiling mounted one.
Your weight is also important. If you are skinny, a trapeze bar that is not so robust may not put you in danger, but if you are heavy, you should consider one that is made out of strong materials and that has robust straps. Nevertheless, if you are not sure, you should check with your physician and see what he/she recommends.