In trying to choose a MOSFET for the project, I researched how to use MOSFETs in their non-saturated region. Modern MOSFETs are optimized for switching so their saturation regions are small and their headroom when non saturated is limited so I decided to use an old MOSFET. I chose an IRF640 as I happen to have a bunch of them. Next I plan to test out how they behave in their saturation region which is how MOSFETs are used in audio amplifiers. I will also be using a separate opamp for the current sensing resistor. I have a spare TLC271 which is optimized for single power rail usage so that is what I will use. More when I have built the test circuit.