Generic/clone of smartwool sox seems to be board fave for cost effectiveness.  

You might have to consider boots with more insulation, or perhaps a different style of boots altogether.  Sox ony do so much, and the insulation on the boots makes a big difference.  200g insulation is what the mil considers "Intermediate Cold", FWIW.

Even if your boots are GTG as far as their own insulation, you can only add so much sock inside before your foot becomes cramped.

You did not state your locale/temps/activity level, and all these parameters make a difference.

I will say that here in RI, 200G insulated boots with good sox do not make it if one is static.  My GI black bunny boots work very well, although they are a bit heavy.  I prefer them to my older Sorels, as the GI boots do not need daily wool liner changeout.

As far as the black bunny boots go, a good, foam, runner type insole insert (adds insulation) and some thick sox are GTG for most anything except very active running and such.

OTOH, a slightly longer and wider version of your current boots, with runner's foam insole added might be able to accept thicker/better sock/liner ensemble.

The same principles that work on your body work on your feet.

Winter, use a thin synthetic boot liner then layer to a heavier wicking sock. The idea is layer, synthetic in so it doesn't overheat allowing the wicking action.     Wicking is very important, wrong setup, your feet can be warm as toast then once the sock gets wet, they feel like they will never be warm again.  

Yes, wool retains some of its insulation properties but it wicks for crap and that some will freeze your butt off if they are wet.  Keep the moisture away from your skin.  The socks you have are probably pretty good as most boot wool snythetic blends are designed to use the best of both principles.  You're probably only lacking a liner.

BTW, You can go to the sporting goods department and buy polypro of nylon but if you aren't squemish women socks the same blends are 1/3 the money.  Warning, if you do the womens thing, careful the wife doesn't keep them all come laundry day.

Tj