Haircut with appropriate layering is a good step. It should cut down on knots and tangling. If you think it may be caused by scarves--why not stop wearing them for a short time and see?? If so, you can avoid them, or choose to tangle.
I'm assuming "quite thin" means fine?? as you say it's medium density. In that case, protein should be your friend. I'd try a PT and, depending on what you use, a DT to follow. My fine/low porosity hair loves protein. I do one PT a week and use a lot of products with protein. For me, protein helps to tighten curl, reduce frizz and add volume.
Depending on where you live, the dewpoints have dropped significantly. I live outside of Philly and the dewpoint was 23, I think, yesterday. That's low for this time of the year. You need to add moisture in your products to make up for the lack of moisture in the air. That means that I add an extra layer. When the dewpoints are higher, I use a leave in OR curl enhancer. When they are low, I use a leave in AND a curl enhancer. Always follow with a jelly product (gelatinous consistency, minimal or no chemicals.)
3a (Corkicelli), highlighted, fine, low porosity
modified CG, since April '07
CG since 3/11/08
HGs: Anything Sevi; Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; UFD Curly Magic; Botanical Spirits Jellies, CJ Repair Me