Looking for suggestions: Non-dress watches you can wear as a dress watch?

Holly smokes 9-5 in a suit!   Much respect to you...

When I used to use suit and ties ..I paired it citizen Caliber 2100.

Just enough dress and just enough sport.

Truly anything that is not too large and fits under the cuff, from a Rolex Explorer, Tudor Black Bay, down to a DressKX. Even many field watches would be a possibility.

A vintage looking diver is elegant and sporty enough I think!

A vintage chronograph or vintage diver on a quality leather strap or bracelet will do just fine. If you're looking for a newer piece, find one that's 40mm or under. It will slide under the cuff a lot easier. The PRX fits the bill of being a sports watch that can be dressed up. Some Hamilton models are not dress watches that can serve the dress purpose. Take a look at the Jazzmaster Seaview Quartz. 

The PRX PowerMatic 80 has the waffle dial which is very nice, would fit the bill.

Otherwise, vintage sports-type watch and/or chronograph for me.

So many options...a midsize sports watch on a bracelet (think OP34/36, etc) looks good with darn near any outfit. I've chosen this over my dress watch at times because it just looked right.

I have a blue Gentleman for that reason. I will throw it on a leather strap, now it’s ready for my suit and tie days. I keep it on a bracelet, now it’s sporty. Slide it on a nato, let’s go on an adventure or casual days. It has 21mm lugs. I find the leather straps that fit no problem on Amazon. I use 22 nato straps so I can use them on my other watches. I had two nato straps from bark and jack, only one did not become snack for my Great Dane. Rest in peace Blueberry Broad Weave.

Alpina Alpiner GMT. Wearing it right now. 41mm, but thin profile and a wing span that's not crazy. Quartz as well. Grab'n'Go for dress and travel.

Man that looks cool how much did you pay for this beauty?

Hard to beat a classic, dressy diver. The new Aquastar Deepstar II fits that role pretty well. 

I actually have this coming, might work well for smart as it’s a world timer. Might change the glass, but not straight away. Then I just need to get another skin diver for casual.

I think vintage styled "dressy" divers are the best bet, like the Oris Diver 65, BB58, or CW C65. 

A close second would be modern divers, like a CW C60, Pelagos, or Oris Aquis. 

I recommend: https://www.jomashop.com/longines-watch-l37594766.html

I know this answer comes very late, but i figured i'd still answer 😅 No, i don't wear a vest, only a shirt under the suit. Indeed, a vest would look a bit "too formal" (i'm a financial advisor, so i try to look formal, but friendlier than a lawyer)