What is the purpose of the new camera? Family / vacation pictures, or professional photography?
Based on your post, it seems like you are familiar with photography - probably cut your teeth on 35mm SLR's.
Lightweight body typically means plastic - but that's hard to find on a full-frame sensor. Why the need for a full-frame sensor? You can save a ton of $$ by going with a consumer-level DSLR like a Nikon D3300 or D5200 and still have the ability to manipulate the camera settings to your liking.
In my opinion, unless you are a pro photographer, there really is no need to go with pro-sumer or pro-grade cameras. A good photographer - even a hobby photographer can take beautiful picutures using any of the DSLR or mirrorless consumer-grade cameras out there. Save some money and weight!
-Z-man, pleasantly happy with my Nikon D3200.