Your feet will sweat in rubber boots regardless of whether you are “sweating” or not. Its fine if its really wet outside the boots, but you have to take it into account regardless, if youre going to wear those. 30f isnt cold per se, but its plenty cold for damp feet to feel cold. Ditch the cotton socks, wool or synthetic only. Make sure socks and boots arent too tight…anything that reduces circulation even a little will make you cold. And if your feet are cold, add a layer around your core and put a winter hat on. You lose a lot of your body heat through your head, and if your core starts being cold your body will reduce circulation to your extremities, so that hat is keeping your hands and feet warm.
At 30f (and even colder) i use the “non-insulated” rubber boots. The neoprene in the boots is plenty warm, I dont need additional insulation until its much colder than this. And I am not a particularly “warm” person. Imo if you have cold feet in +\- 30* temps with a pair of neoprene rubber boots, the problem is something other than the boots themselves.