thebodyshop.com/en-gb/hair/hair-brushes-and-combs/natural-curl-comb/p/1083792?ds_kid=92700059550456171&utm_placement=All%20Haircare&gclid=CjwKCAiAp4KCBhB6EiwAxRxbpMaG2TPG8tQ0HdaSwieq_WannQ6lvKQwcmeWfStLmAMcxCQouF4muRoCUZgQAvD_BwE&gclsrc=aw.ds
Start with one of these and some leave in conditioner. Gently tease the knots until you can run the comb through without any resistance. Then use a finer comb, but go VERY gently.
You can always try sleeping in a bandana as well. You'll still need to comb in the morning, but less so.