Hi friends. I have 2 of these bed / workstations if anyone can find a good home for one or both of them. We have disposed of the mattresses as they have been used, so you will need to buy a new one. Mattress size is 1890mm x 770mm (which is about 6'3" x 2'6").
These are known as "small single" or "shorty" mattresses and they cost about £50 ish to get a new one (one possible place to get one is B&Q as shown in the link below, but you could probably find it cheaper if you were to look):
https://www.diy.com/departments/comfy-living-2ft6-open-coil-sprung-mattress...
One of them is complete with all the parts, screws and instructions to assemble it (the picture was taken before we took it apart)... reminder, no mattress with either for hygiene reasons.
The other one is missing one of the three little drawers you see in the picture (although I am doing my best to try and find it) and is also missing some screws, but I know which ones they are and I don't think they would cost you more than a few £'s to buy and I can tell you which ones you will need. Smoke and pet free home.