So, thanks to an earlier MTB purchase (I'd gotten a Motobecane from BD, but I bought it too big) I had a one-step up from the stock SR/Suntour fork. This one actually has lockout, whereas the stock one did not. Having lockout will suffice for now, until I can afford an upgrade to a better fork.

(I thought that the Motobecane had a tapered head tube, but after tearing it apart I discovered it did not. Yay for me, as that made it compatible with my new bike.)

Thanks for all the replies and advice, I learned a bit about MTB forks that I previously did not know (again, previously I was a former BMX racer and road cyclist, current big-wheel BMX rider).