As you have not yet started pool training, (read the post folks), see if they can rent you the type you eventually want to use. In your case a BP/W.
A BP/W is a bit different to use. The differences are small, but you might as well train with the type you will use.
If they only have (all integrated) back inflates, use it as if it were a BP/W. Which mostly means set the shoulder straps (loosely) on the pool deck and then leave them. There are adjustable BP/W straps, but most find them unnecessary.
If they only have jackets, you may be able to pick up a BP/W before your open water dives. But then treat whatever you use in the pool as much like a BP/W as you can. DiveRite has good ones non expensive ones that your shop might carry. And simple is all you need. See many threads on 'getting a BP/W'.
Good luck, have fun.