Input protection circuit with P MOSFETs and SPDT for ON-OFF switch
If you do not want to compromise on any of your design requirements this is what you are going to need.

The resistors may not be absolutely necessary, but when hard-switching between rails it's always better to have them, to limit current rush into the gate capacitance, which may degrade the channel. But you can put the one single resistor in the gate-path of the mosfet, no need for two in each leg of the switch.

If you want you can add a small NMost in stead of the switch and two touch pads:







simulate this circuit &ndash; Schematic created using CircuitLab

But that is entirely just for added spiff-factor. No function at all.

Your original schematic should, at currents up to 5A with low (but not ultra low) resistive losses in the MOSTS, not cost too much more than $5 to $7 though.

With regards to the fuse being all the way at the start, those are quite good instincts. I don't know the type of battery, but a TVS may also fail at some point, I have seen one or two go hard to ground at failure (they shouldn't, but hey), which with a good battery at least one MOST will start smoking as well.