I'm dealing with this on my 12-foot skiff. It's plenty hot, and will be until the end of November here on the Texas Coast. I have had many Bimini Tops on boats and they're great for shade, but are very much in the way for doing anything else. I have decided to use a 5-foot wide golf umbrella, just to use after I'm anchored, and fishing. I think I'm just going to mount a couple of pieces of PVC pipe on the sides of my middle seat, that I can drop a piece of 1" wooden dowel into, with a piece of PVC on top that will hold the umbrella handle. I can put it up when I'm fishing, and quickly take it down to get underway.
I've seen a mount that is basically a swivel seat mount, that you sandwich between your swivel seat mount and the seat mount base. It has an arm that extends out and mounts your umbrella. So, you can swivel the umbrella 360 degrees around your fishing seat. Lots of machinery, just to hold an umbrella. And, over a hundred bucks!
My boat is way too small for a T-Top, and they don't really provide a lot of shade for anyone other than the helmsman, and virtually none when you're fishing. So, I think I will try the cheap-o umbrella mount on my skiff.
Good Luck! Island Jim
I'm an Eighth Day Adventist. On the Eighth Day, God went fishing!