I found it terribly difficult first thing around and my lactation consultant was worth her weight in gold. She was encouraging, she explained a lot, she checked latch, she gave advice, and more than anything else she let me forgive myself when it wasn't right for me. I didn't bf for very many weeks but without her I'd have given up within a few days. And her info meant that next time I was prepared, and I was successful.
Throw it back in your partner's face, ask him how much of the breast should be in the baby's mouth? What happens if it's only the nipple? Where should baby's nose be? Their chin? Can he explain the significance of the soft palate? How will he know if the latch is bad? What's the best positioning for a blocked duct? How will he know if baby is getting enough milk to keep him healthy????
Then remind him that men CAN induce lactation and you'll order the hormones for him online so that he can grow the boobs to do it himself.
In all seriousness, since you probably don't want to start a fight, gently tell him that breastfeeding is nothing like sucking on a straw, latching can be complicated so it's really not common sense, and that you do have unique challenges so you need to make sure baby will actually have enough to eat (this last bit is hopefully so he sees it's about baby's health, not about your comfort). My gut feeling for YOU is that you won't have even half the issues. But it is a skill to learn, and it isn't magically natural, babies do know how try, but that doesn't mean they'll attach in a comfy way, we mums need to be taught.
Then begin with asking your midwife (now) about breastfeeding support. Midwives themselves offer this to some extent and are there to help you, and will signpost you to a lactation consultant (probably also NHS & free) if there are tricky times in the beginning. Normally they wouldn't kick you out of the hospital until you're able to get baby latched ok and have fed them. I know this because... dun dun dun... despite my "success" with last kiddo, I've since had surgery on my breast, meaning I don't know how it will go, and when I asked if I was likely to have trouble, she told me there's bespoke support! Really glad I asked now so that I know I won't be abandoned. LOTS of us find it tricky. You are not alone and not silly in the least.