Have you considered a vintage sewing machine? They usually have a larger harp space, are inexpensive, last forever and are easy to find. The downside is they are heavy. A Singer 15-91 is said to be an excellent FMQ machine. It has something to do with the way the bobbin sits that is supposed to make it work so well at FMQ. There are Japanese made models from that era that should work well, too and they would usually be less expensive.
bkay
This one is a really nice example: (Note where the tension is. The similar Japanese models would have the tension in the same place.)
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