6 amps isn't very much. Especially when considering start-up loads.
It just might work though, since the motor specs state that it only pull 840MA
Hook it up to a thermistor. (works like a thermostat)
Put the thermistor between the jacket and you.
If you find a fancy thermistor, it will be adjustable.
This will cycle the pump off and on so you will stay in your confort zone.
I hope this helps.
Best of luck.