Since I'll be here for a month, I took my time and checked out the prices of several shops before deciding where to buy. Today, I went to Martelli's Glove Factory and bought a pair of navy blue leather gloves with silk lining.
I wanted to get magenta or a bright blue to match the fedora, but the shop lady said that one should either wear a bright hat and understated gloves, or an understated hat and bright gloves. She recommended the navy color, which I bought -- though I may still return to get a bright pair, too. This is what they looked like when I first bought them, and here's a photo after a year of use:
Some people come to Florence and buy jewelry on the Ponte Vecchio, maybe even more come for the designer shoes, but my favorite souvenir is a smart pair of gloves.
Update: I did go back for a bright purple pair: