Well water alone isn't going to necessitate an insulated tank. Is your water exceptionally cold? Is it exceptionally moist in the room being remodeled? Those two factors are usually what you look at when being concerned about sweating.
However, unless those two things are true AND the toilet is going to get an exceptional amount of use, flushing over and over and over in an hour, like in a restaurant bathroom, say (more correctly, a POPULAR restaurant bathroom), this isn't a concern in modern low-flow toilets, and here's why:
As you know, sweating is caused by very cold water chilling through the china to make it cold on the outside of the tank, and, in a very moist environment, the water in the air condensing on the cold tank.
In a Toto low-flow, the tank fills to hold several gallons of water, even if it is going to only use a little more or a little less than a gallon in the actual flush (the rest of the 1.6 or 1.28 gals per flush is the water used to refill the bowl). It holds several gallons, but it only dispatches, say, one in the flush. Why? Because the weight of the extra water in the tank causes a higher water pressure going through the flush valve, so you get a pressure boost from that extra water, even though it doesn't exit the tank.
Because the tank doesn't empty on each flush, any new water coming in to refill the tank will necessarily mix with the water already there, thus moderating the effect of new cold water being introduced. If it's a while before the next flush, the water will be at room temp by the time the cycle happens again, and thus no worry about sweating. Also, because the tank is only pulling another 1.28 gallons from the water pipe, rather than 3 or 5 gallons, the water coming into the toilet will likely have been resting in the pipe in the wall for a while, again acclimating to room-ish temperature. Let's say you have 3/4" PEX water lines in your house. 5 gallons/.0184 gals/linear foot = 271. So the water in 271 linear feet of pipe is required to pull that 5 gallons. The water in only 70 linear feet of pipe is required to cycle a 1.28 gpf toilet.
So...the water going in is likely to be warmer, and it's mixing with water already in the tank. Unless you are flushing the toilet a whole heck of a lot (and the toilet is in a moist, un-air-conditioned room), sweating really isn't an issue.
In the Toto line, only the Drake (and lesser Carusoe) are available with insulated tanks. I think that Terry said that he had sold some in like Alaska.
Want a skirted elongated toilet? You have a lot to choose from! Do you like the looks of the Carlyle II (which I have)? I think it's excellent! How about the Soiree, Guinevere, Vespin, Carrolton, Nexus, Vespin, Carolina II, Legato, Lloyd or Ryohan? Look them up online and check out the photos until you find one you like!