Totally different situation to yours, but my bub goes between boob and bottle all day long. That's not to say that we've had no problems at all, but we're still BFing almost six months later!

Has your DS had a bottle before? I take it he hasn't had formula before? I don't know, maybe you should try him with some to make sure he's okay with it. Or on the day get his carer to mix half EBM and half formula in case he doesn't like the formula too much. Or he might be fine with the formula and you won't need to worry at all!

Don't stress about him coming back to the boob, he'll be so excited when you whip them out, you'll feel great (if a little like a milk bar!)