I wouldn't bother with formula at this age - formula isn't really needed after 12 months, so why introduce it so late into the piece? It's not for nutrition (cos your boobs are taking care of that if solids aren't filling those gaps) and if it's comfort she wants then why toy with what's going into her belly? That's a bandaid that anecdotally won't even stick. DH's hear all sorts of things, usually from other DH's who aren't first hand experiencing the wakings, either, so he needs to trust you and your instinct with this one.
My two are both BF, DS is still feeding and some nights will sleep through, others he will come to my bed for snuggles and babu. Giving him a banana won't 'cure' him from wanting me when he's feeling anxious or in need of reassurance.
If your DH wants to help, tell him he can explore other options and ideas as if formula didn't exist, because it's akin to changing the oil in your car when the fan belt's squeaking, i.e. two different events when the oil may not even need changing