DS gave away the high chair a few months ago, if he won't sit on a big chair he is given the option of sitting in the chair or the high chair. Sometimes he even chooses the high chair!
He refused to sit in the pram from early on but recently has allowed me to use it again. If he resists I explain what we are doing and when he can get out again, this is good enough for now.
The sling is a good idea. Get one that supports your back so you can walk for long periods of time without pain. I have a ring sling that is fabulous, I have a bad back and it's never my back that gets sore, even after hours of wearing him. It does hurt my shoulder after a while though.
Giving toddlers choices helps them to feel a bit more in control of their lives. Can you introduce choices in other areas? (not an open question, that's too hard- something like "do you want the red shirt our the blue one?") It might help.
(just don't ask about the car seat

that is a nightmare I am yet to find a solution to.)
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