I am also a 16+ (currently wavering between 16 and 18 on hips but a 16 on waist) and I buy all my retro underwear from What Katie Did, so they do cater for 16+. Their bullet bras are fab and go up to a DD/E and their suspender belts are a little cheaper than the one you have found and very comfortable - I have the pull on one and it really holds well.
I don't have a corset yet as I am still saving but I can highly recommend WKD for all other stuff.
Additionally their sizing is really clearly explained and the staff are incredibly helpful.
The other place I buy underwear, although not vintage style per se is
www.figleaves.com. They have a good range and for a little extra will send you your purchases wrapped in tissue and a tiffany blue box with white ribbon - fabulous!
Good luck and please share if you find anywhere else