Hybrid bike - would like to switch to a single front chainring, what are my options?
I suspect you'll be buying a whole new crankset. You may also need to upgrade the bottom bracket as there's not much choice of upgrades if you're starting with square taper parts. 

My hybrid had a very similar drivetrain, including suntour cranks/chainrings which were riveted together. 

You've already got a fairly wide ratio cassette for an 8 speed (I run the shimano equivalent) so you might struggle to get the range you need. Perhaps something like 11-34 (the widest range I've seen on 8 speed) with a 32-36 tooth chainring would do it. 8 speed casettes are cheap and consumable so swapping out to get the extra bottom end might help you. The alternative of going for a full 1x9 system would of course mean a new shifter and probably cable. 

You should probably make up a spreadsheet of all the gear ratios you have/use and those you'd get in your 1x8 suggestion. And you can try running just in your middle chainring to see how much too hard 38 is. 

The actual weight saving though, on a hybrid which probably has a heavy frame, is unlikely to be worth it, every assuming better/lighter cranks to go with the reduced chainring weight.