I feel like a pretty cool addition would be making the Dizzy’s Underground facility a bit more hostile once the protagonist starts getting heavier. This came to me recently when I was interacting with the staff at the facility while barely mobile. It doesn’t have to be crazy but some fattening events or some fattening trickery going on would add a lot more flavour to the facility at higher weights. I am thinking something similar to how the village in the legendary game “Lipomancer Ruins” functions. It would also create a bit more of a difficulty level in the game that could be fun.
It’s possible you’ve already thought of something like this or dismissed it before but I figured I would mention it here anyways. I love the game! It’s been one of my favourites for a long time. I’m excited to watch it continue to grow! (No pun intended)