Is it just the 2 of you going? When I booked a room for 2 in the Cheyanne they gave us a room with just a double bed and no bunkbeds

Or maybe you could push the bed against the wall under the window, ie away from the bunkbeds, that would also give you more floor space in one area rather than the narrow gaps between the bed and the end wall?
When me & DIL took GD I rang and asked if bed guards were available, the CM on the phone didn't understand what I was asking for, I got an email confirming a cot would be in the room

There was a cot in the room which GD wouldn't go in so DIL ended up using pillows round the edge of the bed! That was at the DLH!!
Not having had kids myself (inherited older stepkids lol) I've never had to buy one but don't they come in tubular sections that slot together and then the fabric part fits over? Just wondered if they would collapse small enough to fit in a suitcase so you could take one with you just incase?
You arrive the same day as us

If you are on the Eurostar you'll spot me no problem, I'll be the one with enough luggage for a fortnights holiday instead of 5 days