I am starting to wonder if controlled crying for naps is my only option. It's not how we've parented so far but for his sake, he needs better quality day sleep and I need to not be in pain. What would you do?
I wouldn't do controlled crying. But I can also say with equal certainty that I wouldn't do carrier naps (not least because I have had significant spinal surgery, but also because I'm funny about needing physical personal space).
The reason I wouldn't do or advise controlled crying at this age is that its replacing the comfort of being close to you with no comfort at all. When older, after 12 months or so, baby has more dexterity and can better develop ways of self-comforting by using a comforter object or doing ritualistic, rhythmic movements to themselves. These type of fine motor skills don't usually start to develop until 9 months or so, and I'd leave until at least after 12 months to be sure.
Having said that, there are much gentler ways to achieve the same result by 12 months old, especially so if you start making the progress towards independent sleep now.
will only nap if latched on the whole time (which hurts after a while!). Even then, lots of the time his eyes are not properly closed and he doesn't wake up refreshed. We tried a dummy persistently from around 3 weeks and he wouldn't take any, MAM were the closest but he never took them properly despite being a very sucky baby.
Its really clear from this that your baby likes to comfort suck. I would find a way to make comfort sucking work to get some independent sleep.
You are unlikely to get a dummy accepted at this age, so I'd stop beating yourself up about it (but if you have another child in the future, it might be worth considering earlier).
Some babies suck on material. I've known babies who suck on muslin squares, the ears of their teddies, a corner of a blankie - all sorts of things. Baby is young to be able to coordinate movements to do this yet, but it might be worth setting up for when older.
Other children suck on their hands - fist, fingers, thumb. You could help baby by holding babies hands in such a way to comfort suck (?maybe - I don't know anyone who's worked on getting thumb sucking established, so I am speaking theoretically)
There's also the Pantly Pull-Off. Its not a quick fix but will help you take steps in the right direction towards independent sleep.