I'm trying to use a mosfet transistor to create an amplifier to boost a square wave up to around 8v. The problem I am encountering is that the load resistance connected to the drain terminal is very small, around 3-5Ω and this is limiting the gain of the amplifier which I want around 20. Would a BJT or FET voltage follower between them be enough to make this work?

 

A Mosfet makes a poor voltage follower because its gate voltage must be much higher than its source voltage.
Use one transistor (not a Mosfet) for voltage gain then use a power transistor (not a Mosfet) for the high current that is needed.