First of all, IMHO there's nothing wrong with mixing tires. Yes, the RFTs are stiffer.
Most of us don't like RFTs. So my advice is to let the RFTs wear out, then replace them, possibly with the same tires as your fronts.
Most of us on non-RFTs carry some kit. I use Green Slime because it claims it can be washed out of the tire, so it can be repaired.
And the pressure warning (TPMS) works regardless of the type of tire, provided the appropriate stem (with transmitter) is installed and you don't use a metal cap.