Oh it sounds like a shitty situation you're in. Let us know how you get on tomorrow though.
FWIW I mix fed first time and stopped bfing at 8 months and still regretted it after. At some point though it will be right for you to stop and you mustn't feel guilty at all. I have never got on with expressing so I do sympathise.
What do you think has changed to make your supply suffer this time around? Is his latch not great maybe? Maybe it's him and not you IYSWIM?
Have you had him checked for tongue tie at all - just popped into my mind and can't remember if you mentioned it. This would make bottle feeding much easier for him and would explain alot. My nephew had it and after the snip at 2 weeks old was like a different baby.