I have this problem too. I wear my hair down when I sleep (less stress on scalp AND hair for me) I flip a satin sheet over my pillows so it's not like I haven't looked into that option. My hair dislikes oil and goes crunchy when I use it, and trust me, I have tried many oils, but they aren't for me. I have found my hair just likes to be clean and me using a light conditioner, sometimes with cones, sometimes not. My hair likes variation. Trims or no trims doesn't matter for the tangles problem at the end of the wash cycle.
I use a sulfate shampoo, (diluted) once again my hair just likes to be clean, if I condition without having used shampoo first it goes stringy, tangly and just a plain mess. (CO wasn't for me...)
What I have found to delay (I'm saying dealy, not cure) the problem is damp bunning and/or a tiny tiny amount of leave in. But I wouldn't recommend damp bunning if you live in a colder climate. Oh, and it hasn't got anything to do with humidity in the air, I can have tangly hair a cloudy moist winter day. (we have the rainy, windy and cold costal climate here)
I can totally relate to your problem, in my in the case, my hair just likes to be clean.