I was in a similar situation a few years ago: a terrible haircut (kind of mullet-like) that had some layers that were no more than 1.5" long! I went for haircuts every 2-3 months with a stylist I trusted who grew it all out to chin/above shoulder length looking okay, and have since been growing it longer. Now I go for a cut at Devachan every 5-6 months; she's really just cut my back hairs (which are 2b-c, and stick out from the bottom of my 3b hair) and barely shaping the rest while it grows in. It's taken some time, but my hair is healthy and finally back where I want it to be, length-wise . . . nearly there, style-wise! Just be patient, it will come, even if your hair is fine. I do recommend using a silk scrunchie to pull it back, as this will minimize breakage.
3b, fine, medium density, normal porosity
Wash: Phytolisse and Shea 10-in-1
Rinse-out: CJ Deep Fix, Phytolisse, Shea 10-in-1
Leave-in: Phytokeratine, CCCCL
Styling: Phyto hair curling stuff or Deva Coconut Supercream (which may turn out to be a HG for me!)