I haven't printed my own work at a "standard" size in with either analog or digital processes for years. That said, I learned early on how to cut matts, windows, etc. both with dedicated cutters and a straight edge and razor blade, even bevels. It's a skill that still serves me well.
If you are looking only to flush mount and foamboard will work, get the board with heat-activated (drymount tissue) already coated on the board. In the past two years, especially with my canvas projects, the ease and efficiency of the workflow has been marvelous and as a bonus, there's been no issues with a chad of tissue making its way between the print and the board.
I don't think that there's coated 2, 4, & 8 ply boards, though I could be wrong, but the foamboard is available in many sizes, thicknesses and colors. Costs a little more than uncoated, I think, but well worth it.
Once mounted, you can easily cut it to size and I'll bet if you find a good supplier, they can cut it to your specs for a nominal charge.
For my 4-ply boards, I have the windows custom laser cut to my specs. I'll bet the same company will sell you pre-cut boards to your spec, though it will be more expensive than doing it on your own, but a lot easier, more consistently in size and cut, etc.
That company is framedestinations.com in Texas and they ship quickly once ordered. Used them for 6-8 years now and they make presentation a snap for me.