Also easier in this particular situation: use a 5V (or a bit higher) power supply - like a USB adapter - and a regulator to get it down to the 3.3V your Arduino needs.
Another thing: is there anything on the 3.3V Pro Mini that can not handle 5V? After all it's still an ATmega328 processor. Those level shifters may not be necessary. What would happen if you power your Pro Mini at 5V over the Vcc/3.3V pin? That should bypass the regulator.
Can't try that out myself as I only have two 5V Pro Minis, this as I wanted to be able to test stuff at 5V, normally using NodeMCU or ESP12E modules which all operate at 3.3V. Most sensors nowadays indeed operate at lower voltage.