Rehabbing Double-hung Windows?

Our first floor has a total of seven double hung windows in the dining and living rooms. They’re cottage style, meaning that the top windows are shorter than the bottom. I really want to rehab these windows to have double-pane glass, and a more effective jamb system (they currently have the original rope + window weights system).

I’ve seen sash replacement kits that provide an all new sash (window), and a tilt-out jamb-liner mechanism. I don’t really like these systems, because even though they’re wood, the sash looks totally, well, new. We’re not likely to paint the interior window trim (I spent too much time stripping the trim down to bare wood…), so I want the wood to match.

I want to preserve my existing sashes if possible. My plan has been to take a single sash and see if I can a) retrofit it for thicker glass, and b) retrofit it with new tilt jambliners. If it works, then I’d do all 7 windows.

Has anyone done this?

I am concerned about the old sashes being able to accept the increased weight of thicker glass. And I’m a little concerned about whether the new jambliners would require me to reframe the windows because they take up additional space in the jamb – and I don’t think I can really cut down the sashes.

I’ve only found one supplier for tilt jambliners, and their catalog is pretty lacking in information about exactly what parts one needs to order (this is a window replacement-part supplier.)