I wasn't too sure about this bit, but obviously know very little, hence why I was asking: "Similarly, when the crust becomes lighter… it can float a little higher." I also thought isostatic rebound was when glaciers melt and was wondering if this is different?

Isostatic change can occur where any weight is added (sinking) or taken away (uplift). Bangladesh is the recipient of a lot of sediment from the Himalayas that is causing the crust there to ‘sink’ causing coastal regression there.