insulation makes the world of difference, never heard of this 'liquid' but I would go with the insulation mats. Once the kitchen is fitted you wont notice the height diff. Depends on your budget, always nice fo a tiler to have an open floor but you will save a bit by fitting the kitchen first and ufh/tiling second. (kitchen fitters to allow for extra height of course, sometimes end panels can be left off until after tiling, I say sometimes)