think that I might possibly find a mountain bike that fits me better than the one I have right now.

Am looking at getting the Specialized hardrock 650b later but it has the gears.

So to get the best bike that fits me with the benefits of SS which are countless, could I use a kit such as this on it?

https://www.amazon.com/gp/aw/d/B017KS5RE8/ref=cm_cr_arp_mb_bdcrb_top?ie=UTF8

Also here is the bike

https://www.specialized.com/us/en/bikes/mountain/trail/hardrock-v-650b/115480

And could I save more and get a better bike by converting a geared only to SS?.