Hi J.,
I SOOOO feel your sleep deprivation. You have my story 9 months ago. I too did not want to CIO, I was ready to breastfeed until 2 years, we did the co-sleeping thing... everything. And my daughter was a HORRIBLE sleeper. Since day 1! She hated being laid down alone, she wanted to be held, she wouldn't sleep more then a few hours... she started to sleep better and then went through a growth spurt around 10 months and everything was awful. I was a walking crabby zombie!
Around 14 months I NEEDED something to change. I was impatient and felt like I wasn't giving my best to my daughter because I wasn't taking care of myself. I decided to determine if the night feedings were REALLY feedings or if they were comfort measures.
I really paid attention for a couple of nights to HOW my daughter nursed at night. Was she really eating like during the day, or was it light and not much actual swallowing and drinking. I determined that it was significantly different then her day time feedings and felt very strongly she was only nursing for comfort.
So, after about 3 nights of the same thing... I decided it was time to wean her off night time feedings. There were other ways I could give her comfort and let her know I was still there. The next night when she woke I went in, I checked her diaper, changed it if it was wet, took her potty (we followed EC practices and now we are in full blown potty training, but that's another story), then took her back to her room sat in the rocker and rocker her and cuddled with her. She DID ask for milk. I just calmly told her it was not time for milk, but mama would rock and cuddle. Sometimes she would ask me to sing to her, so I would. (we sing a lot in this house) It took about 3 nights, but eventually she didn't ask for the milk any more. After about a week, she didn't wake up anymore in the night!!!!!!! :-) It was the first time I had gotten 8 hours of solid sleep since before I as pregnant!!!!
In addition, she started going to bed easier. I no longer had to rock her to sleep. We could have our cuddle time, and then I would say 'mama is going to lay you in your bed now' and then I would and she would be fine, and just go to sleep.
She kept her day time nursing sessions for awhile, but soon started weaning herself. She finally dropped everything at 18 months. I really don't think weaning her off middle of the night feedings had anything to do with it. She's a VERY active little girl, a good eater (NO trouble getting her to eat solids), and very independent. She just decided she was done.
My horrible sleeper is now a great sleeper. She does tend to be an early riser...but she does at least sleep 11 hours at night and then takes a 2 hour nap during the day.
This too shall pass.
Try to find some time to rest during the day. It really helps. Maybe have your older daughter have some quiet time in her room when the baby naps...and then you rest too.
I congratulate you on extended breastfeeding and doing things naturally. It's so important and gives our little ones such a great healthy start.
Good luck!