For needles, I use size 18 to size 22, and most of the time it's a 22. They should be needle system 135X17. For thread you can use nylon or polyester which should be at least size 69. I switched a few years ago to all polyester thread in size 92 for normal sewing. No belt guard only means it's an older machine like mine that didn't have one when I got it.
No one lives forever, the trick is creating something that will.