In my case, the Crescent 6-ply rat mat is 4.2mm deep and bevelled at 45° (pretty much standard everywhere now). The aperture is right to the very edge of the Ilfochrome image (no cropping). Thick mats in any of the white tones are considered avant garde (meeting the museum-grade conservation standard) and certainly are not cheap.
My framer uses a sort of CNC cutting set up which is set up on a PC from input measurements (everything is variable, including the bevel) then the mat material is laid down and the program does the rest with just a few mouse clicks. It is very fast and swift as opposed to doing it all skillfully by hand, which was the way my first framer in the country did it (he had 50 years' experience).
LED lamps are making an appearance in hardware and lighting stores; quite interesting, but the illumination has been observed as either very blue or intensely white.