Unless it's changed since I bought mine (a long time ago, to be fair), the boot is the right size for the stated size (so a size 40 (EU) is roughly as you'd expect to fit a foot that normally takes a size 40) and *you* have to go up one or two sizes to accommodate the thicker socks. (Hope that makes sense!) I went up two sizes, but I've got wide feet so maybe best to try before you buy, or get them from a company with a good return policy.
My boots were just the outer leather without any inner liner or padding (apart from the collar, which was padded) and a wooden insole. I got a pair of felt insoles and wore thick hiking socks in them. It took a while to get them broken in but they were great for hiking in all sorts of wet and mucky conditions. In the end, they dried out while left with my parents and sadly were beyond rescue.