Hi there,
Welldone on getting him to resettle! It's great when you have a break through like that.
As you are so close to weaning age, I personally wouldn't give formula as in a few weeks food will start to help out. I'm not being snobbish about breast is best, as I give breast and formula to my LO due to a low milk supply. I would have loved her to be solely breast fed. Are you doing night feeds with a bottle? This might make those night wakings easier.
I have a 5mo and she started waking every few hours and I kept on feeding and resettling but she wasn't taking full feeds. I therefore knew she was waking out of habit more than hunger. In my research I came across The Core Night method. Essentially after the dream feed (or waking up) the baby shouldn't be fed again before 4am. Obviously, you don't want to starve your baby, so I normally start resettling and see how much resistance I get. It worked really well for us. I never had much success with dream feeds, as it really disrupted her sleeping pattern (and she would wake every couple of hours after) so I let her wake naturally. However, if she wakes again I resettle her now without a feed. There was a bit of resistance at first as I was breaking a habit but she now does 1 night feed and wakes around 6.30am.
in my research other causes for night wakings are too much nap time during the day (from your post, I don't think this is you). I think Tracy says, no naps over 2 hours.
In the baby whisperer there is a section where Tracy discusses a baby who needs less nap time. I was trying to get my LO to take long lovely naps, but she's really not interested and never has been a big daytime sleeper. She's bright eyed and bushy-tailed after shorter ones (she is completing sleep cycles). I get one big nap a day and two 45mins. It makes following EASY impossible, but she refuses to nap for longer and is ready to play after recharging her batteries. I went through a patch of resettling her for longer nap, but she really fought me and if She did go down, she slept less at night. I hope you get good long naps, but if your baby is happy on shorter ones and is completing sleep cycles.... I wouldn't worry too much about it.
Best of luck!