Non-isolated current sensing, on a delta load?
Those are conflicting requirements, you can't do it.
Only if the load is fully balanced, you could get away with measuring only two phases in a delta connection, and calculate the third.
Now:
If you don't have space for CTs, can you use a hall cell solution? What is your current range?
There are some hall cell current sensors, good for 30 amps, available in a SOIC-8 package, which is no larger than what a shunt resistor would be. And fully isolated for 2 kV RMS.
Check the ACS712 datasheet.