If you can get a vintage Singer 237 Fashionmate -
I think it is a great simpler, mechanical machine.
Features: straight stitch
zig-zag
three needle positions
forward and back
one can lower the feed dogs only on the later versions of that model
Down side: it weighs between 35 - 40 pounds, so while moveable, that might be difficult for someone that is not very strong.
I liked this model well enough to have purchased six of them.
When buying any used machine, make sure it works before buying it. I have several machines that still "work" well enough for basic sewing, but some of the featured stitches are no longer accessible.