After a lot of experimentation, and mainly by accident, I finally found my almost ideal paper - Harman Matt FB MP Baryta. It's got a lovely matte, slightly chalky surface which is smooth and prints with a range of colour and contrast that reminds me of Epson's very expensive Hot Press Natural paper.
Having bought one packet of this Harman Baryta, I find that it's now been discontinued and replaced by a range of gloss barytas, in conjunction with Hannemhule. So I'm searching again for a good matt baryta paper, with a fairly white coating - rather than the greenish tinge of Canson's Rag Photographique or the slightly glossy surface of Ilford's Gold Fibre Silk baryta.
Assuming that there is still a company that caters for people wanting smooth, matt baryta papers, does anyone know a good replacement for my Harman stuff?