I would at least put a ledger board at the back, and have a framed wall at the front.
You can set the ledger and the front wall to level, a little higher to lift the tub above the floor, and then set several piles of mortar down, set the tub down on those and let the mortar squish out. When dry, those will support the base of the tub. You can't hang the tub from the top unless it's also supported from the bottom of the tub.
If you plan to shower there and tile around the tub, you will need some flanges at the wall to divert water back into the tub. Those can be installed with Silicone.