Welcome to Tropical Fish Keeping forum.
We have other members in Arizona, they will probably be chiming in eventually (in summer many are on vacation
), and they maintain successful tropical tanks in similar conditions.
Goldfish are one option, but bear in mind that they need a lot of space. A 55g may seem big to you, but it is not big to the goldfish. And they produce a lot of waste which impacts the water quality and thus the fish.
Tropicals will depend upon your tap water parameters. Some fish have preferences, others are more adaptable. Telling us the hardness and pH of your tap water (assuming that is the source water) will allow us to suggest options. You can find this info out from your water supply people, many have a website with water data posted.