I live in Cuba, so online shoping for me...Thats a pretty looking DLG, I hope the build turns out well.
You can maybe find light weight balsa online, search for "competition balsa" for example... https://www.nationalbalsa.com/Aero_Light_Balsa_p/116348ct.htm, but depends where you live I suppose...
but in some strength critical areas you might still want to use heavier balsa or balsa ply anyway...
I've found balsa ply to be a very strong compromise between weight and strength.. just go really easy on the glue, 3 ply balsa, alternate the grains, and clamp it well. I used that for the bottom half of my rudder and the wing-tips).
Is that tail boom 100% balsa? is there a fiber-glass rod in there also? or are you going to glass the outside?
I think fiberglass rods can be too flexible, I have them in some kites, and they seem flexy... try to get hold of a wide diameter tube instead of rod. bigger diameter = less flexy.
I have 5mm carbon tube which I am not sure is enough... but the Pug's spar seems less than 5mm diameter tube and seems ok.
My last glider is a sloper with 3mm spar plus a coupe of balsa stringers for extra strength... it seems pretty stiff wing and is also about 1m span, I'll dig up some pics.
one thing can make a big difference in weight is to get the servos and electronics as far forward in the nose as possible, that minimizes how much extra nose weight you'll need to add later to balance it for the CG.
Also you can get away with small lipo battery but still a long flight time... my 220mah 1s lipo battery is only 6g but good for about 40 minutes or so.
i am using a 2s 300mAh batetery and 9g servos with a 5V 2A BEC. this is the lighter eectronics i could find.