Marcos, I use my Singer 15-91 for everything from silk up to 1/4 inch of leather, denim, etc. It can handle #69 thread and Bob at Toledo will tell you these are good machines to start out on while you save up for other machines. You're not going to saddles I assume, and I just sewed a guitar strap that was 7/8 oz veg tanned, foam, and 4/5 oz chrome tanned for backing. I couldn't even get the presser foot down completely. It just does what I want it to.
I have the one below for sale in a cabinet and another one that will be for sale after I rehab it (yeah, I kinda love and collect them). The one below is a centennial model, has the blue and red tag instead of just the brass one. So I want a little bit more for it. If you're interested pm me. Cheryl