I am looking for a circuit that can reverse a DC motor( 12V/3A) with a +15VDC signal using mosfets. I have used contact closure and solid state relays but they have proved to be troublesome. Please advise.
Monolithic H-bridge drivers are available from competing manufacturers. You can also acquire monolithic H-bridge motor drivers, such as the LMD18200, in the power range you seek.
ST Microelectronics' VNH2SP30-E - Automotive Fully Integrated H-Bridge Motor Driver is one you could look at. It's so integrated that all you'd really need to control it would be a SPDT On-Off-On spring-loaded rocker or bat-handled switch.