I've got 24v fans and and and a handful of 24v e3d heater cartridges so I should be good on that end.

Thanks for the link I was searching for a bit (not explicitly on this forum but google) as the mosfet was my first idea but wanted to find some sorta confirmation that it should be fine to setup in this manor.

I'm currently running a single extruder 300x300 printer entirely on 12v but looking to switch over to 24v.

With plans to get a new bed plate laser cut and run a 120v mains silicone heater but not wanting to wait i'm looking for solutions for a temporary setup to switch now.
I've got a few of the standard "trigrorilla" mosfets sitting around and was originally wondering about using this in a similar method to a SSR by running the board and steppers off 24v with a 24v signal switching the mosfet and running a seperate 12v power supply.

It was suggested by others that I may be able to use some sorta combination of pwm adjustments and PID to run the 12v bed off the 24v power supply through the board without using a 2nd PSU or external mosfet?

Parts I have that could be used:
30a 12v psu
21a 24v psu
15a 24v psu
bunch of random external mosfets (unfortunately no SSR's on hand)
I do also have a 24v bed here that I had ordered which would have made this easier as a temp solution but its far from flat so i'm really trying to not use it.

Unrelated but to give context - I'm in Florida where we are stuck indoors due to a massive storm/hurricane heading through the state so i've got plenty of time to do this now but ordering parts or going to the store isn't all the easy to say the least.