Other people can correct me here if they disagree, but I'll share my perspective...
Let's just say Hudson was sleeping 12 hours through the night right now... it's nice to pretend
... anyway, if he was, he wouldn't be getting up to nurse in the night and your body would correct the supply of milk it produces overnight, so you'd have enough milk to feed Hudson during the day, and at night your milk production would slow. So... feeding him formula at night (if you think that is best) would kinda be like him just not feeding at night, so as long as you're still nursing throughout the day, it shouldn't cause too much disruption.
Some of the concerns though:
-if you switch to night time formula, you'll have to stick with it, because your supply at night will really drop off
-switching to formula at night won't necessarily solve the problem of gassiness since breastmilk is the easiest on his digestive system, he may have added gas when formula is introduced...
Another option for you:
-generally you will have the most milk in the morning, and since your son only feeds on one side, what about pumping on the other side while he nurses? His sucking will activate your letdown, so the milk will flow easily, and you can probably gather enough for 2 bottles if you pump the first two feedings of the day (say 7am and 10am). Then, at night, you can give him this pumped milk? This is just an option if you don't want to go to formula...
Let me know what you think!
Jana