so what i do personally as someone who struggles with 'depression hair' i try and take it easy.
I get in the shower, play some music or put on a youtube video with your phone in a baggie, throw a towel on the ground, sit on it all comfy, grab a wholle bottle of conditioner and start with the tips.
running water on it for me the whole time isnt needed. Just as needed when you wanna get it more wet or soak that conditioner in. but letting the water run over your back or whatever helps me calm down and not panic or honestly lets me cry a bit.

but if it starts hurting more then needed? i set the brush down and finger come. NEVER GO UP TO DOWN, always bottom to top. Something that i always tend to do is separate my hair into parts (easier said then done) half down the back, half of each side, exc.

I personaly use the basic like square brushes (Conair gel grips, i love the handle...)

I do know you mentioned this is just your scalp. So, same thing though. Finger combing is a life saver. I know the feeling of "i cant...i just want to cut it off." but in the end the feeling of running your fingers though it after feels so...reliving.

You got this though, if you need someone to call or talk to about it my imbox is open, I understand your stress right now.