>>2041947 (OP)I've been commuting in smart-ish clothes for years now, with a foldable bike. Not full suits but at the very least chinos and polo shirts, often shirt and jacket.
You will need fenders front and back, ideally with a rubber skirt if you can find one for the front. Not so much for puddles but for tiny debris that can end up on the lower hem of your pants and get it spotty and dirty.
Look for a bike that will have you ride upright.
Ideally, something that has a chain guard as well so you don't risk staining the end of your pants' right leg. Clips as mentionned by others are a good idea. You have some velcro bands out there for this purpose. I see a lot of people using these while dressing in your typical business casual attire so I guess if you fold your pants in correctly as you put the band on, you should be fine and not create creases.
Depending on how hilly your area is, maybe you'll need to look for something with a few gears in order to deal with climbing without breaking too much of a sweat. You can also wear some armpit protectors if you know you tend to get sweaty quickly. It's not the most comfortable thing, sure, but it can save your shirts if you know you tend to get sweat rings quickly.
Also, ALWAYS carry some gloves and a handkerchief or two in case you derail or whatever. Just trust me on this. It will eventually happen and you'll be glad you can protect your pants with the handkerchief and remove the gloves "inside out" so you don't get guff all over yourself.
Oh and keep a comb somewhere, in case it gets windy.