Well done on coming this far with breastfeeding! I too am exclusively BF my DS and he is almost 7 months.
I can empathise with your wanting a break, I find it doubly hard running round after a 2.5yr old as well as feeding my DS. It takes a lot of stamina to continue...esp with those night wakings! You are lucky that your DS takes a bottle of EBM as my LO doesn't want a bar of it. We offer him a little water after solid meals and he generally just chews at the nipple and gets a dribble every now and then!
Don't feel guilty about supplementing if you feel you'd like to. Easier said than done, I know, but you have given your son the very best start he could get and a bottle here and there won't do him any harm. I think you just have to watch for any allergies in the first instance but it should be smooth sailing for you. I would like to put my DS on a bottle for the night feed as I feel by the end of the day my supply may not be enough to get him thru. He was waking up to 4-5 times but now down to once or twice (if we are lucky!) My biggest worry is the initial accepting of a bottle instead of boob... So I will be facing the same thing as you soon, just gotta take that first step and get the courage up to do it. Sorry lots of rambling and little advice but I'd love to know how you get on!