We solved the problem of wavyfloors - sometimes feels as though we are at sea! - by putting down mahogany underlay with two or more coats of varathane. It is screwed down and the screws show but could be coloured. It is quite handsome, cheap and easy to install. I am careful not to spill much water and to wipe it up quickly lest it go in the cracks. a wavy floor is not suitable for ceramic tiles. Our house is very downscale! But it looks nice and is comfortable. I have wonderful friends with creative suggestions on how to do things well but less expensive. Wish I could send them to you!