Sounds like you have learned a lot and made good progress! Are you getting a light lather from your co-wash and ending up with 'squeaky' clean feeling hair when you are rinsing?
You might try a combination of scrunch and pump with lightly running lightly coated palms over the surface of any areas prone to frizz, not enough to press or pull out waves like raking. IIRC they run palms over in the Devachan videos on YouTube, tho only upside down you could do it both ways up.
Not sure there is any solution to the part issue, if you want hair super neat you use a comb and sacrifice clumps or wave, if you want volume and curl closer to the roots you sacrifice a neat line. People who can do both generally have a strong curl pattern. I quit parting my hair when I established that was contributing to canopy frizz and killing curl, other wavies I see who part have straight roots too.
Growing your hair out differently or cutting in layers differently may help your hair to sit better without a part. It's easier to adjust clumps into good positions if you don't overdry with plopping or scrunching and use root clips. Some people clip before they plop, no idea how that stays in tho.
2a-2c, medium texture, porous/ colour treated. Three years CG, growing out mechanical and chemical damage = breakage and very high porosity. Past armpit length heading for waist.
CO-wash: Inecto coconut
Treatments: Komaza Matani, coconut oil, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume, Inecto argan
Styler: Umberto Giannini jelly, Boots Essentials gel
Experimenting with: going back to basics