I just finished Floor 10 on Easy Mode (which was still quite hard if I'm being honest xD )

But then Floor 11 was just a harder version of Floor 1 again. Does this game keep looping endlessly or is there an ending that I can strive for? Maybe even with a boss at the end?

Yes, and the closest thing to an ending is Proving Your Worth and starting a new run. I'd imagine they will eventually release a story mode. For now, I think they should have the current non Save Deletion mode be called exploration mode, and if you turn on Save Deletion, have the normal Hardcore text instead say "Prove Your Worth by challenging the statues and discovering what's beyond the tenth floor's walls.", alongside an item next to the statues to immediately activate everything you need to do said run instead of walking up to each one and going through boxes. They should probably have a drill appear on 10F as soon as you get the compass and a message from Japes reiterating that you should use it north. The way it is now, if you don't prime yourself to get a Drill on 9F and no amount of reloading makes it appear on 10F, you're screwed.