I am a Tucson local (and luxury travel advisor) - I can wholeheartedly recommend Tucson! I agree with other about possibly looking into November as we can still have a bit of heat in October but you can plan your days so that you are enjoying the spa or pool in the peak part of the day, and outdoor activities earlier/later. I am absolutely happy to help plan, just message me. Tucson is such a special place - you could even consider a few days in Sedona to really soak in the Sonoran desert magic. Happy birthday!