Measuring Current in Combination Circuit with a Shunt
There are very convenient modern IC solutions for measuring high-side current. For example consider the TI INA169 60-V, High-Side, High-Speed, Current Output Current Shunt Monitor.  You can even get a breakout-board ready to use from vendors like SparkFun, et.al.

It is generally not desirable to put a shunt in the ground-return side because of possible interactions with external ground connections.  Unless the entire circuit is within your control (no external connections).