Do you do protein treatments? Limp, soft and frizzy can mean overconditioned. Try upping the protein and seeing if that helps.
Thinning could be due to excess shedding from cowashing... it could also be your hair changing over time. Try protein first, see if that helps. If you think your hair is thinning from excess shedding you could try to go low-poo for a while and see if that helps.
Either way, if you co-wash or low-poo, just be very gentle in detangling while the scalp is wet/conditioned. That's when the follicles are at their weakest. It's also a good idea to detangle w/ a conditioner that has great slip. There's lots of good RO's out there that are moisturizing but don't necessarily have great slip. I'm no expert on detanglers but recently I've been using KCKT to detangle and it's awesome.