First of all, I'm sorry for your situation. I know sleep issues are common enough but nevertheless so frustrating!
Second, I'm pro-cosleeping and pro-nursing - but I'm also pro-Mama's peace of mind. Children's needs must be balanced with adults' or resentment and / or exhaustion may follow. My kids (6 and 4) still end up in our bed often but we all sleep well together (which hasn't always been the case). We have had all sorts of arrangements and here's the funny thing; from age 5 months to about 2 they didn't sleep with us near as much as they do now. They both nursed a lot at night but my husband would bring them to me, I'd nurse them, then he'd take them back to their crib (more on this in a bit).
You don't have to sell out your ideals (no CIO) to get something you want, but you might have to be willing to put some work in and get over your ambivalence. For instance the "work" it will take to make a change *is* a lot of work, but you will be better for it.
I believe kids sense ambivalence and react to it. If you try to change your nighttime arrangements but deep in your heart you feel guilty about it (for your son), angry about it (at yourself, your partner, whoever), or unsure, then I personally think it might not go well.
So my short answer is - find a small change you feel sure about and proceed with confidence. Be kind to your son but understand that learning other people have needs (as in, people like his mother!) is part of the growth process.
Joan has a good suggestion: "I would tackle the breastfeeding first, then the co-sleeping, so it isn't a HUGE change all at once." If you could get your body back at night you might not mind having him need you for just cuddles. Some weaning theories suggest going to "once a day" or whatever (which worked well with my kids when the time came; they were weaned at 3 and 2) but I think at nighttime this wouldn't work well (everyone is too sleepy to enforce / cooperate). I'd suggest starting the mantra, "we nurse in the daytime" and being firm about it at night. Now this will involve some work but mostly, you'd have to be sure about it before you adopted the new program.
With my kids, I night-weaned them at 18 months. I just started telling them, "We nurse in the daytime". It worked well - probably because when they woke asking at night, my husband settled / comforted them. It also worked well because I was sure this was OK to do; I didn't feel guilty. I was ready for longer sleep at night. I'll also add that I was OK with the night nursing up until then so there was no backlog or resentment by the time I started. I was ready for the change.
My husband did the night duties with the kids, or did most of them anyway. Let me tell you why this worked for me. First, A. it gave my kids more time with their father, and more balance for my children, B. it made the "kid workload" more fair, C. it honored my husband with the loving work of parenthood, and D. kept my resentment at a zero. I understand other families don't make the choice to let the non-caregiver parent take nighttime responsibilities, I'm just saying that really worked for us.
Best of luck - be kind and gentle to yourself!