I have made a helpful framing guide for you. My art prints are extremely easy to frame and its very easy to find affordable high quality frames that will fit.
I use standard 'A' paper sizes A4 and A3 on all my art prints.
A4 Paper size - 210 x 297 mm
A3 Paper size - 297 x 420 mm
Look for standard A4 size or A3 frames. You can also find good frames on online just search the size of the prints such as frame for A4 prints or frames for A3 size prints, and you will be able to see a big range of frames.
If you need any more help get in touch and I will be very happy to help you. Best Wishes, Haidee x