New Ladder For High Sleeper Bed

[yinyang]

We've got a Thuka high sleeper bed in my daughters room which currently has a sloping ladder but we'd like to replace it with a straight ladder to give her more floor space.
Thuka do sell a straight ladder conversion kit for £215 which seems a bit much when the only bit we need is the ladder.

We don't mind if we have to buy a different brand ladder and improvise how we attach it but I'm not having much luck tracking down any straight high sleeper ladder to buy on its own. Has anybody done this in the past or can point me in the right direction. Thanks in advance.