Hi, I'd defo get a matress-Argos do quite decent ones, the mothercare ones seem a bit thin but my dd has always slept really well in her travel cot. I think she sleeps well as they're fairly enclosed compared to a cot bed which can seem pretty big to a baby!
get a mattress - they're very thin anyway, but otherwise they're sleeping on a plank also if it's 2nd hand, check that the bottom of it lies flat - we've been given travel cots in hotels that have bagged iwth use so that the central leg pushes up in the middle and the rest of it sags away, meaning the baby rolls off to the side. awful things.
I'm thinking about when my 9 week old is too big for her crib but not old enough for me to be comfortable moving her into her bedroom. We have a cot bed ready in her room but it is too big to move into our bedroom. We have been given a travel cot but I don't know much about them and have one burning question. Do you need to buy a mattress to go with it or do they just sleep on it as it is?