Can I leave baby for a day without too many supply issues?

Just a quick question. I've got a spa day booked for when my son is 8 months old, obviously he'll be eating at this point too, but I want to continue to breastfeed also. I absolutely can't express (I've tried everything, seriously, everything) and I'm happy for him to have a bottle of formula during the day at that point if I'm not with him. Will not feeding him during that day cause any major supply issues? Or will I be able to simply continue as normal afterwards? I should be able to give him a morning or evening feed. Thank you! Xxx