You’re being prudent, Matt. Skin cancer is nothing to take lightly, as you know all too well. I’m far more careful than I was years ago, and many clothing makers have dedicated themselves to making apparel that resists sun well.
First, some definitions. Some clothing companies use SPF ratings, which measure the garment's ability to stop UVB rays, the ones that cause a sunburn to hurt and turn red. But others include UPF ratings, which keep track of both UVB rays and UVA rays. UVA rays can also cause skin cancer.
My go-to brand for sun-beating clothing is ExOfficio. They make a wide range of clothing for sunny pursuits, from pants to shirts to hats. In particular, I like their long-sleeve Air Strip Lite Shirt ($85). It’s comes with a comfortable cut, sleeves that roll up easily (and can be secured with sleeve tabs), a ventilated back, and two generous chest pockets. ExOfficio made it with a breathable, quick drying nylon/polyester blend that's rated to UPF 30, meaning you can stay in the sun 30 times longer with this shirt than you could if you were bare chested. A normal white cotton T-shirt, by way of comparison, has an UPF rating of around 5.