I’ll be interested to see what, if any, leads develop here. I had the same problem – that is, even the “large” wigs in styles I would consider were tight on my head. My (male) hat size is 7-1/2, a ways beyond your average woman’s cranium. Wearing a wig more than a few hours was an irritating experience – literally. Fortunately, I don’t have the balding issues you describe, although I have lost a bit of hairline. So, over this past hot (!!) summer, I finally said “to hell with it” and put down money on extensions. When they come out in December, my own hair will (hopefully) be at a length I can live with as my mane keeps growing out.
Still, it’ll be good to know where a good-fitting wig, in a reasonable, mature, non-drag-queen style, can be had for my large head. One never knows when a back-up plan may be needed!!