If you have an alcove 1m long, you want something about 90-95cm long to fit into it, to give you max room for the baby.
40x90 is crib size, I think, so you could look for a wooden crib. Try John Lewis or Asda. It's a shame Mothercare is gone as they were good for things like that. DS2 despite being tall fit into a 90cm long bedside crib until he was about a year old, 40cm is really narrow though, and I think he would have complained about the sideways room if it was enclosed. A lot of the bedside ones are about 95cm long but about 50-60cm wide which is better. And they can be standalone if you don't want it by your bed.
This is quite an interesting listen if you want to know where this "baby only sleeps on me is a modern thing" comes from:
Essentially it's a bit backwards - babies traditionally did sleep with their mums until some meddling blokes researchers came in and decided this was all a bit risky - well it was in Victorian/slum Britain, fair enough - and decided babies ought to be sleeping through the night by 3 months old. This is then achieved for generations in various ways including formula, early solids, sleep training, over-dressing, front sleeping, and even drugging (opium, alcohol, prescribed sedatives) and you get a cultural norm that babies should sleep through and should sleep independently - then more modern science has come in and correctly denounced a lot of these methods as being harmful, leaving mums in a bit of a quandary where you're told they should be sleeping etc but you don't have any tools left to do it with (and then there are newer products with the same old or new risks e.g. Sleepyhead and so on) - so then more modern parents are starting to say hang on, why are we trying to force sleep anyway, what if we just left them to it? But in a way it's not modern at all, it's going right back to what was originally done. But that's why it comes across as a modern idea to our parents' and grandparents' generation.
If you don't feel comfortable co-sleeping that is OK of course - but it's still worth knowing how to set up a safe co-sleeping space in your bed, in case you're in the situation where the baby literally won't sleep and you're worried you will, simply because by avoiding co-sleeping if you are in an extremely sleep deprived state you can end up doing something much more risky like accidentally falling asleep on a sofa. This is why they have now changed the advice, it always used to be don't co-sleep, it's now if you co-sleep, follow these guidelines. It is sometimes more risky to try very hard not to co-sleep. You can always move the baby (or yourself) when you wake up if you do set up a safe space and still despite efforts accidentally fall asleep in it.