Your machine is metal, no plastic gears anywhere. You can do some basic maintenance on that motor before jumping to one with high amperage (if some is good more may not be better): 1. remove the brush covers and remove the brushes, 2. remove the silver tubes at each end which house a grease wick (with maybe a spring at the top end to push the wick down), 3. spray out the motor with CRC QD electronics cleaner, 4. make new grease wicks (I've sued wool felt) and saturate with grease (Tri Flo or petroleum jelly), fill the ports under the tubes also, reinstall, 5. wipe off the brushes very carefully, reinstall with covers. I have a small inverter that runs off my 18v battery system for power tools which I use when testing a motor, rather wreck that than catch the house on file. If/when you test the motor use a circuit breaker protected power strip. You might be happy with the Singer motor.
Also when sewing heavier materials you need to use a heavier needle and larger thread.