Big A-type ladder is probably enough.... If not, there are good aluminium ladders available with 3 joints. Those can be put up like A or middle part horizontal,or somewhere between. They use such ladders in construction work or putting up wallpaper etc. You can't get very high with those, but maybe high enough.(posted 8815 days ago)The pose of a standing model is not so relaxed and natural, so maybe it is not very good idea to put the bed against wall....
Sakari