And actually...
The rules say that with only a PPL your rights are to SHARE the total cost with your passengers...
So you can not sit as a non-paid F/O without a CPL doing to this fact.. but you can sit as a F/O and share the cost with your passengers.
You ALWAYS need a typerating or be on an approved typerating course to log flight time. In a piston airplane below 5700 kg you still need a "class rating" like SEP Land or SEP sea or ME ... and so on.