Yea. That isn't a high temp reading. I have a v8, with the aux cooler, and when it is 99 degrees where I live I get similar temps.
220, higher, then you start to worry. But you won't see that unless your towing a lot, up a huge hill, for a good bit.
It really, really, really, really, sounds like your just looking to blow money on something. Doesn't need to be this.
The trans Temp is far more externally linked and the designers knew that. It is going to be a much more flexible system temp wise.
Did another up and down mountain run last night, driving the wife to a company retreat through the TN/NC mountains.
Only difference was this time we had had to do it at night due to logistics. It was 60-58 degrees the whole time and my trans temp never got about 158 degrees.