Sorry about the confusing title but I need help and I don't know how else to describe my dilemma!

I am trying to deboss the letter B on a leatherette piece that is 0.75mm thick. I have a 3D printer so I want to create a positive mold for the deboss side (outside side of the leatherette) and a negative mold for the emboss side (inside side of the leatherette); think about it as a leatherette sheet pressed between two plastic parts where one part is an extrude boss of the letter B (the positive mold) and the other is an extrude cut of the letter B in a block (the negative mold). However, the negative mold has to be 0.75mm larger all around to accommodate for the thickness of the leatherette when sandwiched between the two molds.
:

I don't know how to do this: I don't know how to create an extrude cut of the letter B in a block that is 0.75mm larger all around. If I simply increase the font size then the whole letter increases in size include the two U shaped holes of the letter B--but these two holes need to get smaller by 0.75mm. (Please see the attached image.)

I hope I am making sense and I am really looking forward to any helpful feedback. Thank you!