How can I get the book from the bed in the locked room?

You need to stop the bed from flying up, obviously.

Fix it in place permanently.

Do a little construction.

Try nailing it down.

If you don't have them already, get the coffin nails from the crypt where
Stan now has his office.

Then just use them on the bed.  If you have the mallet from the cemetery,
Guybrush will automatically hammer them in.

You will also need another nail.  You can find it in the hotel.

Go into the other room, and you'll find it sticking through the wall.