The first thing to consider is if baby is getting enough calories over 24 hours? This means frequent, big daytimes feeds that baby gets most of his calories during the daytime.
I was formula feeding by 5 months with my youngest (although was EBF 2 of my older children at this age, so have experience of both). But this meant I was able to actually see how much baby was drinking, in a way you can't when breastfeeding. My DD was taking about 6oz (so this is a full feed, according to recommended amounts on the formula tin, not a snack-amount) every 2 hours from 7am-11pm. I cannot overstate enough that this is a lot of milk, very frequently, throughout the daytime.
So if baby isn't getting the calories he needs in the daytime, he'll need them at night.
Next is to completely disassociate feeding and sleeping. Feed downstairs and after the feed have a bath or whatnot, so that baby is awake when going into the cot.
You can also disassociate feeding and sleeping in the daytime by feeding when baby first wakes up from a nap, rather than when going to sleep.
Then al all sleep times (bed and naps), do your settling in the cot with the dummy. Given you are using a dummy (and assuming baby does take the dummy for comfort sucking), no need to rock in your arms. I would just keep a firm hand on baby's chest/back/side and keep shushing and reinserting dummy.