165 mm crank arms will likely feel better with your short legs. I wouldn’t expect them to make a huge difference, but they will help fine tune your bike fit.

The SRAM S300 is a nice crank. I have one on a fixed gear and like it. It comes with 48 tooth chain ring, but you could easily swap that for a smaller one. The Sugino Messenger is a good option, and there are many others. (S300 has 130mm bolt circle, so you can get 42, 44, 46… whatever you want). The stock GXP bottom brackets don’t last very long, but they’re easy to replace, and better ones are plentiful.

For single speed in a hilly city, I’d want a ratio between 60 and 70 gear inches, or maybe in the high 50s. That works out to 42 chain ring and 16 or 17 cog, in other words, what you have now. If you want a slightly lower gear, nothing wrong with that.

The WI Dos is a great option. You could pair the 17/19 version or the 20/22 with a 42, 44, or 46 chain ring. Any of these would be good. That freewheel isn’t cheap, but they last forever.

Another cool setup is to get any old double crank with a BCD that will allow for chain rings of something like 39 and 41 teeth. Get the Dos freewheel. Put the crank on a bottom bracket that will give a good chain line, and you’ll have a pretty versatile 2-speed. Shifting requires a tool and takes about one minute. You can pick your ratio according to your needs on each route. This is what I have on one bike. Inner gears are 39x19 for 54 gear inches, and outer gears are 41x17 for 64 GI. Since there’s a difference of two teeth at both the front and rear, the axle position in the frame does not change. (By the way, tug nuts are not necessary in any case.)