Hello. I'm planning to tear up a creaking poorly-laid chipboard upstairs bedroom floor and replace it with engineered flooring. The flooring is 22mm thick and can be laid across joists. It's mdf with a 6mm oak layer and tongued and grooved all round. It comes in three varities, unfinished, brushed & oiled and lacquered. Any advice on which type to opt for? If I glue/screw/nail the flooring through the tongues, would this type of flooring need an expansion gap round the wall as I assume MDF is completely stable? Last question, could I lay something like rockwall in the floor void to provide some sound insulation? Would there be any benefit to doing this and is it allowed in building regs? Thanks for any advice.