can you buy any changing station to fit your cot, or does it have to be made for the cot specifically?
Do you mean like a changing topper that just sits on to of the cot? We got a cotbed in M&P but there was no specific cot top changer that went with it so we just got a plain white one there too. It just sits on top of cot and could be secured with a velcro tie. I don't think you need a specific one at all.
Another option is if you have a DIY DH like I have who made the changing topper for our cotbed. We are still using it everyday and will for No2 as well. When we went to get the cotbed etc - he was "I can make that no need to spend money on it" (he loves a project)
He was very proud of himself