>"When I get paid on Friday, I'm sinking $100 immediately into a sun shirt, sun gloves, and a neck gaiter."
If money is tight, go for a very wide-brimmed hat and something like a bandana for added protection for your neck/upper sternum, but I'd skip getting a special shirt. I've NEVER gotten sunburned through a shirt, ever if it wasn't laboratory tested to SPF50. Unlike sunscreen, the shirt never rubs or washes off. So I suggest wearing ANY long sleeve shirt, including a loosely woven one when it's hot, rather than a short-sleeve shirt.
And certainly for garden work and potentially on the trail - get what the professional gardeners get - a very wide-brimmed straw hat. A few bucks at the garden center. I work with geologists in the Southern California desert at times and they all have one in the field gear.
In China (the big, mainland one) people wear long-sleeved shirts AND white cotton gloves to avoid tanning when outside. Walking down the sidewalk, riding on a scooter - lots of people had white gloves on. I found I needed to do that on a kayaking trip in Baja - out all day in tropical sun with water splashes and the sunscreen just wasn't doing it. The lightest gloves worked great.
I retire my old collared dress shirts into sun shirts. When I want the cooling sweat to be retained like a summer GCNP hike or garden work. If it might turn wet and cloudy, I wear synthetics, but for guaranteed sun & heat, those shirts cover all my wrists and my neck while being very breathable.