Re: Spring is here!
Wow! I love the way you did the bee.
As for standard sizes and pre-cut mats, you might think about getting a basic mat cutting system. I often cut my own mats especially if a crop is needed or I worked to an odd shape, then lay it out within a standard frame size outer dimension so I don't need special framing.
The mat cutter I bought is the Logan Team System 2 - just a guide rail and slant head cutter, from Blick. It's quite inexpensive as mat cutting systems go but it does the job. I think the new version also comes with the straight cutting head that I had to order separately. Some frame shops will sell mat boards too. It's not that hard to cut mats, you mark it up on the back side and cut from behind so it comes out looking good on the front.
More expensive systems have measuring built into them and a board that the cutting rail is mounted to. They're a little easier to use but I was happily surprised at how well the bare bones inexpensive system works. If you're not cutting hundreds of mats you don't need one of the expensive industrial scale ones.