W..
Bottle feeding isn't necessarily going to make your son sleep longer at night. It depends.
No, you haven't missed your window to get him to take a bottle, but you are going to have more luck getting him to transition to a bottle if someone other than you gives it to him. Have there be 1 bottle each day that dad gives (or whoever) of your expressed milk. Make sure he's hungry when you offer. Make sure you are NO WHERE to be found, so you guys don't cave to the crying and initial refusal and give in.... teaching him that he doesn't have to take a bottle.
Unless he has feeding issues (like real, actual feeding issues) he WILL take a bottle, if YOU transition it correctly and if it's a priority for your family.
How long is he sleeping now at night now? Are his night feedings "full" feedings or is he using you for a pacifier and comfort instead of getting back to sleep another way? Eating "a lot" can be quantity (which indicates hunger), or it can be small amounts but many times..... which is behavioral as opposed to hungry.
Does he use a pacifier?
Typically at 3 months (I think) you should be feeding at 10:30 or 11pm and then again around 4:30 or 5am. But 6 hours is the longest stretch you could expect. Not sure what he's doing now.....
You can stop offering him ANY food between 10:30 and 4. Monitor what he's eating throughout the day to make sure he's getting enough and make sure you talk with your ped to make sure it's ok for his height/weight.
Good Luck.