Preparing a 4.5yo for surgery?

[butternutty]

My DS is due to have his tonsils and adenoids out next week. The hospital gave us a story to read to him nearer the time (about a bear who goes to hospital so that he has an idea of the process), but I'm starting to panic a lot bit about how to prepare him.
He knows that his tonsils are a problem for him, and we've had light conversations lately about different family members who have had their tonsils removed and how much better it made them. I just really don't know how to approach it - if I give him too much advance warning, I don't want to stress him out, but at the same time, he doesn't take it well when we spring things onto him.
I wish we could get it over with - I feel sick with worry. As well as preparing him for it, I'm worrying about the op itself, his recovery, and how I'm going to cope with entertaining my 2yo as well when we can't leave the house for two weeks. DH is taking a couple of days off work, but after that I'm on my own.
I've searched the archives on here and seen a lot about keeping on top of pain relief after the op itself, but not much else (if I've missed other useful threads, could someone bump them please). Any advice or words of wisdom? Thank you.

[jetSTAR]

DD1 had grommets earlier in the year and we just talked fairly matter of factly about the whole thing. I was honest about the fact that there would be a needle that might hurt a little bit (but in fact there was magic cream!) the main thing I kept repeating was that I would be there all the time with her while she had her 'little sleep'.
I know tonsils etc is a bit different and more painful (I had mine out as a grown up!) but personally I think being honest and straightforward about it and answering their questions image way that they can understand is important. I had to repeat myself lots of times as she kept wanting to know the same information! She was 4.5 as well.
Good luck and I hope it all works out fine