Your curl pattern seems similar to mine, I am also dealing with chemical and mechanical damage exactly the same as you, never heat styled.
I find the more I wear my hair straight the harder it is to get curl - putting it up wet when I am in a rush or brushing for second/ third day hair pulls out the curls nearest to the roots. Sometimes it takes three washes to get my hair to curl back up again properly. So it's better for my wave pattern to rewet/ rewash and wear my hair curly every day.
I get better curl when I don't shampoo at all, I can get my hair 'squeaky' clean 'lathering up' with loads of a cheap conditioner (I use Inecto). Also get more root curl and cleaner roots washing my head upside down and scrunching in every product, including those that are washed out.
I'm afraid I am also still learning about my hair and suitable products. My hair absolutely loves coconut oil as an intensive treatment tho, it is supposed to reduce porosity and help damaged hair retain the structural proteins. I CO-wash that out no problem, usually rinse and repeat. If you really prefer shampoo you might try coconut oil shampoo (aka Movie Star Method), there is a long thread over on the Long Hair Community. Shea butter is too heavy for my hair, I think it better suits those with a really strong curl pattern.