I "think" by "pressing board" you mean a quilter's sized ironing board?
Mine is 22"x50"x3/4" regular plywood and screwed onto a metal ironing board. I covered it with several layers of flannelette. Then the top cover was a fun quilting cotton. Each layer was stapled in place.
With time, the top looked sad .... stained and even worn through in the most used position where I press the smaller blocks. Removed that and converted it to be removable with elastic around the edges.
Later stapled the "silver stuff" (not insulbrite, think it's called teflon?) as the top layer. It lets larger pieces of fabric or quilt tops slide/move better. Whereas, yardage or a quilt top tends to stick to a cotton top and then when you press and try to move for the next section, it can sometimes be a real annoyance!
If I were making my board again, I would make it a wee bit wider, so that 1/2 WOF would fit across the width of the ironing board. Likewise for whole FQs to fit on top. Yes, technically most will fit the way it is, but it means aiming well! Another annoyance!!! Luckily I don't work with many FQs.
The length of my board fits nicely for pressing a full WOF and leave space for the iron to sit as I reposition. If you are mounting the board on top of a portable ironing board, you need to watch that the whole thing will be stable and not be tippy once you get it completed. That would only be disastrous! I think that was why we stopped at 50" length when mine was made.
Good Luck in making your ideal ironing set up!