It may not be the chair but how it's positioned in terms of height. Look up ergonomics on the web to find the best position.

RSI is not caused by chairs. It's caused by awkward arm and hand positions held for a long time, or muscle tension held for long periods of time.

1 - Check that the chair, table and machine combination height lets you hold your wrists straight while you are sewing, with your shoulders relaxed and your feet flat on the floor.

It's going to be surprisingly low. Lower the table or raise the chair.

2 - Learn to sew with a minimum of hand grip and wrist twisting.

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This shows typing, but it's the same for sewing ... it's all in the wrist position

And to get that wrist position, it's the chair and work surface ... in your case the sewing machine's bed instead of the keyboard.