There are USB-C docks that you can get that can provide pass-through power and that will work with 12" Retina MacBooks. I have one of them, an OWC Travel Dock E (the 'E' variant has Ethernet) that I bought for use with my 12" Retina MacBook.
Here's a description of it:
https://eshop.macsales.com/shop/owc-usb-c-travel-dock-e
It plugs into your laptop by a very short, permanently-attached cable. It gives you two USB-A ports, a HDMI port, a SD card reader, a Gigabit Ethernet port, and a USB-C port (power input only) for connecting your charger.
I don't know if you want to spend $60 on a dock, but I thought that I'd let you know that there there are workarounds for the "only has one multi-use port" issue.
Note that if you are thinking about other docks with pass-through power, that's fine – as long as they are plain USB-C docks and not Thunderbolt ones. I believe the 12" Retina MacBooks (any year) are unique in being the only Macs that have USB-C ports that lack the optional Thunderbolt enhancement.