Get your current machine serviced, for sure. I'm not sure one way or the other about sewing through multiple layers of fabric; some machines need tuning up and they work fine again, some were never designed for heavy duty use. You might find the people at the shop to be helpful, just make sure you know exactly what you are looking for in a machine when you go in. If you see a machine in a review that you want to check out in person, you might be able to test it at the store and decide for yourself. I'm not going to throw more personal opinion at you about a specific machine, since I think everyone here will say something slightly different. Besides, it sounds like you've got more info than you know what to do with! Good luck!