By all means replace the thermostat for the superior PRT version (note that there are three different ones available!), but I'd leave the head gasket well alone if it shows no signs of failure. There is no evidence that early replacement prevents future failure, it is expensive, and there is a chance you can make things worse by doing so.
Just ensure that the coolant system (rad, pipes etc) are in good condition, and when you fully service, replace the belt tensioner and water pump (its "O" ring can fail and leak).
All in my humble opinion of course.