An Otto catfish would be perfect for your tank. They are small and a group of 3 or 4 will fit in your 14 gallon. They are much better for algae control than plecos and don't put out as much waste. They also like the same temps as guppies. Also, I would get one more female guppy; for livebearers it is better to have more females than males.
I would do one giant otto. They get three inches, aren't as messy as thicker plecos, and actually do live off of algae. It's their niche. Mine is several years old and never touches anything but the walls and algae-ridden surfaces. Even when I give him food, he ignores it. They don't hide, preferring to stay in plain sight looking like a twig. And they have red eyes. Frickin' awesome.
Not mine. From other site, but identical. Angle doesn't show eye color well. Mine's are orange to red.
Rubber lipped or bristle nose pleco. They will be fine in a 14 gal. They only get to 6 inches max and this will take awhile. These two are cheap and easy to find. Heck if you could pick them up I will give you one of each.
Clown Plecos are fine. Extremely inactive.
Or Ottocinclus, but they need well established, well lit, and heavily planted tanks that cultivate a LOT of natural algae.