For now, setting up several empty cardboard boxes - which you must have, moving as you are, with holes cut in some sides but not all, some stacked - would be a good makeshift "jungle gym" until you have a chance to buy or build an official tree! Cardboard and some packing tape can make a great temporary structure.

Are your cats all climbers or tunnelers? Do they like relaxing up on top of something or underneath it? How many kitties need resting spots? Do they like dangling toys or ones that move on the surface? There are so many options, the "best" tree depends on the cats who will be using it!