Can you recommend a Reliable Compact USB 2.0 Wireless Adapter for NanoPi R2S Running FriendlyWrt?

I received my first NanoPi R2S mini-router today. I was able to get it set up and running FriendlyWrt by following the instructions on the FriendlyARM NanoPi R2S wiki. However, until this step was completed, I didn't realize that this board doesn't have integrated wireless radios, as the Amazon page where I purchased it was somewhat misleading in this regard.

While at home, not having wireless is not a problem. However, I'd like to use the device as a travel router, where wireless capability is a must. Can anyone recommend a USB 2.0 wireless adapter that will work with OpenWrt? Ideally, I'd like one that is compact and is 802.11AC.

I have found a bunch of old threads here asking this same question, and although there are lots of recommendations, I couldn't find any responses where someone had extensive experience.

In the worst case, I'll just run stock Ubuntu and use a USB adapter that's Ubuntu certified.

USB wireless isn't a good idea, not for 24/7 operations (overheating) and even less for AP mode (vendors typically don't test their USB firmwares for that); performance wouldn't be acceptable either (antennas too small/ too close to each other for MIMO to work effectively). A cheap dual-radio AP/ router would be a better solution (and a cheaper one as well).