OK, you might want to put the Netherlands back in then! In the south it gets hilly, and the country's highest elevation in Europe is 322 metres. It's true it would probably shrink to Luxembourg size, though.
Vatican Hill, the high point of Vatican City is 75 metres altitude and would still be above the waves. St Peter's Square, the lowest point, would be submerged though.
(Also, I love how the sea perfectly separates Flanders from Wallonia)
Bosnia W