London to Penzance sleeper with baby?

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Anybody have any experience of travelling on the Night Riviera with a small baby? First Great Western have said that they don't provide cots due to 'hygiene' reasons. The gap between the bunk and the wall in a solo sleeper is 55cm. My travel cot (bought because it was the most compact I could find!) is 60cm wide. The bunk is 70cm wide. They have suggested co sleeping with my baby, who will be six months. Sounds like a bit of a squash to me, has anybody done it? Alternative is travelling in the day and having him on my lap but would rather not do this (London to Penzance is one leg of a Ionger journey). Any advice welcome, Google not really helping.

We have done this. They slept in pram

Ooh didn't think of the pram (i usually carry him in the sling most places but we do have one).... Not sure he'd go down in it for long though...

We have taken our dds on sleeper trains to italy, i shared a bottom bunk with a six month old dd2 who i did not usually co-sleep with. It was fine, but i think i had to sleep on my side, facing her for the whole night. We have also used a 60cmx120cm thermarest on the floor in the same sleeper train. On one train we were able to use the cushions that came off the seat when it turned into a bed to hem her in a bit, not all trains had these, so we just used the thermarest.

Thanks so much both. I think I'm going to try and co sleep with him but might take the pram as an option B. If anybody else has any experiences please share. The customer services at FGW seemed shocked I was considering taking a baby on board!