If you call TAC, they usually don't give you too much grief over upgrades due to bugs. They'll e-mail you a link to download the IOS image based on your current (send them a show version).
Memory could be an issue depending on what IOS you have... for instance c3600-js-?? is Enterprise Plus which is a memory hog. c3600-i-?? is IP only...etc... You'll have to remind them when you send the show version, what feature set you have and to double check memory requirements.
It would help if you actually had the bug number when you called... that way, they'll know what version its fixed in.
Personally, I would go to 12.0(??) mainline. Don't use the "T" train unless necessary.
Mick.