If you want to try a cheap suspension fork, try one. I've never bought into matching a rigid atc with a suspension. It should be within a reasonable difference, but there was a time when a lot of people were pushing the travel on old bikes. Rule of thumb used to be 1/2* change in HA for every 10mm.
My Serotta was originally a rigid with a suspension fork option of 46mm travel I'm running 70mm. Of course the HA was 72* so a little slack is not a problem. Likewise my Trek is spec'd for a 63mm, I'm running 80mm. But I'm a Bomber fan, so I can't vouch for Suntour.
As for Suntour, there are some on eBay that are probably closer to your rigid with a threaded steerer. Here is one that might tick enough boxes...
https://www.ebay.com/itm/Suntour-1-1-8-Threaded-26-QR-MTB-Bike-63mm-204mm-Suspension-Fork-V-Brake-NEW/133596887790?epid=17041841983&hash=item1f1afebaee:g
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I'm far from a fork specialist, but with only 63mm of travel, how much pogo stick can you get, of course there could be a bottoming issue, but hopefully you can take out a lot of sag and that might help.
John