You can just layer underneath the waders. The only really heavier or insulated waders are the neoprene...and they are literally 15-20lbs heavier, harder to get on and off, very form fitting
, don't breathe at all(you sweat in the winter and when you take them off, you freeze!), it is very hard to move and function in them and are just all around uncomfortable for most people.
I have neoprene waders...I hate them, and I still layer underneath them. You can also buy wader bibs to wear underneath...pretty neat, easy to get on and off and seem to fit much better with the waders. Or a pair of thermals with sweatpants or equivalent over top. I have only worn boot foot waders with lug soles, so I don't have any experience with stocking foot waders and wading boots. Seems you should be able to get at least a heavier pair of socks on under the stockings? Lastly, I wear a water resistant or waterproof lined jacket over top of the waders.
I won't even break out my waders until October or so...especially since they are so uncomfortable. However, if I had a nice, light, comfortable pair, they would come out as soon as it was too cold for shorts. Do over dress, because it is hard to take layers off and you don't want to sweat or it defeats the purpose...BUT don't underdress either or you will be cold and you won't stay out as long. It all comes down to personal preference and what each person requires to stay warm!
Good luck and be safe!