Both my Sony NEX-7 and my Nikon D7000 number the photos the same.
Personally, I do not worry about the extra size of the JPEGs. If you are capturing RAW... then adding in JPEG is not significant. However, I work on an iMac, not a laptop for most of my work. My iMac is nearly infinite in capacity for all practical purposes in photography. My MBA has a 512GB SSD, so I never run into capacity issues while in the field.
I almost always import JPEG+RAW (JPEG as original). It is a trick that I learned from Boyer. The rationale is that out of camera... JPEGs almost always look better due to the good JPEG processing in modern cameras. Hence... I use that for the first steps off accept/reject, geo-tagging, keyword, rating, stacking, etc. Then, once i know which photos I want to bring into post... then I will select/all, switch masters to RAW with one simple command, and begin post processing.
The result is that I only due post processing of RAW at the end, once I know which photos are worth the effort. Everything else stays in JPEG and still look great given their relative unimportance.
/Jim