I would get Ultratherm UTH off reptilebasics. The Zoomed UTH reach a much higher temp when uncontrolled (125~130+ degrees), while ultratherms only reach about 110 or so, so it's much safer.
I would not recommend going with a large enclosure like that anytime soon for how you are already having problems and are a new keeper still figuring things out. Large enclosures place many more factors into why a ball python might not be eating, might not be accepting f/t, or isn't behaving normally.
The most important aspect of even keeping a young ball python in a large enclosure is the necessity to add many hides, vines, and just a a lot of "clutter" on the ground to provide many, many hiding spots, "walls", and security for it. And if you don't get it "right", the ball python won't eat, or will have a harder time accepting f/t. And for a ball python who isn't already extremely foody and well-settled, you want to lessen the factors.
It's nice to hear about other people using big tubs for their ball pythons, but it's not necessary yet by any means. For your BP and your situation, I personally wouldn't even bother considering it until your BP is at least 800g+.