I was just wondering why you feel he needs to have a bottle at night time when he breastfeeds fine the rest of the time?
If it's because you feel that he may sleep longer, then now that he's 3.5 months, his stomache should be big enough for him to take what he needs from your breast throughout the day and evening to last him through the night.
It's not that I'm an avid pro-breastfeeder or anything, it's just that if breastfeeding is working for you and your son, why mess with it?
I found with my baby that if she was given the choice, she would always want breast. Therefore when I decided to move over to bottles at around 7 months, I had to stop breastfeeding altogeher.
I have friends whose babies refused milk altogether at a very young age, so at least you're not in that boat! My advice would be to not sweat the small stuff. If he wants breast at 10pm, let him have it. In a couple of months time you'll be battling with weaning etc and you'll long for the days when you could just pop out your boob!!