Our bathroom floorboards were covered with boards (screwed into the original boards), then tiled over. There are various brands, and some are waterproof, and some aren’t. Ours are HardieBacker, which is one of the more well known brands. You can get them in diy shops and online. A good quality tile shop might also sell them if you’re lucky.

My house is all floorboards so the kitchen and bathroom were boarded with some kind of hardboard, sorry I don’t know which, just left that to our son. He then laid porcelain tiles in the kitchen and sheet vinyl in the bathroom. Don’t believe anyone who says you don’t need to board the floor, you do. However I do have laminate flooring in my living room and that was laid over the floorboards and it has fared very well.