Firstly... Don't feel like nursing to sleep was taking the easy way out! CIO you leave baby and do nothing whereas nursing for sleep you give everything for baby's sleep needs!
DS1 co-slept, nursed to sleep and was a bad sleeper for a long time. At 18 months I was miscarrying and could not handle nursing him anymore so told him no when he tried nursing in bed. I felt bad but it took only a few nights of him asking before he caught on.
DS2 is a different story... He is 14 mnths now and sounds the exact same as your toddler. It has been like having a newborn for 14 mnths! I've just started pushing back when I allow him to nurse at night... He nurses to sleep still at about 730-8 but I haven't been letting him nurse again until 2am. He has been fussy and asking but I just cuddle him and he falls asleep soon enough and hopefully will start sleeping better.
So maybe try pushing back when you'll allow nursing at night? See if that makes a difference?