I wouldn't submit 36 months of full statements, unless you think your relationship looks very suspicious.
If you want to submit some in their entirety, I'd do oldest, than quarterly, and the last three to six months. You guys aren't even married, that type of evidence is usually not required.
On another note, you can usually select the type of documents you want your scanner to create, and very large PDF files can be reasonably small in size. Might even be easier to downloads then directly from your financial institution than to scan them.