I sew on my grandmothers old 1940's Necchi. 45lbs of cast iron and it will go through 2 layers of seat belt webbing like butter!

One of the biggest things with heavy fabrics is a NEW, SHARP, LARGE needle and a good motor. Jeans needles or larger is best.

A walking foot is really nice so that the fabric doesn't bunch. But a walking foot can be bought separate if you want to retro fit your current machine. Make sure your new one has feed dogs, forwards, (reverse is really nice but not necessary)and stitch length adjustment. If you buy new make sure it comes with a warranty that won't be voided by sewing heavy fabrics. But you could look for a 1950 or older machine and start there. The new ones-Singer-Phaff--etc in the "sewing stores" are lightweight machines. My moms 1970's Kenmore gets jammed with 6 layers of cotton and ALWAYS had to go for service after dad sewed leather.

PTP's report sounds like you can't go wrong with Sailrite. They are made heavy and seems to have good customer service.

Good luck!