10 speed with a 42 really needs a Rad-Cage or Wolftooth Goatlink. It's a dogs breakfast, starts out smelling dodgy, and ends up smelling even worse. Some have succeeded, but many have found the conversions finicky and less than ideal. It had its day when the only 1x was XTR or equivalent, and people accepted Acera performance from 'upgraded' XT. Not sure if those third party bits fit the Deore deraileur you have though. You could try an 42 with the Deore, but you can run into problems with lack of chain wrap and getting onto the 42 tooth cog - if it works, expect pretty crappy shifting onto the top cog.
This leaves the 28 chain ring - a good option if you don't mind loosing a bit of top end speed. Its cheap and easy to install, but only gives a little advantage over 30.
IMHO The best option by far, is upgrade to an 1x11. You need is a cassette, derailleur and shiftier and chain, so not cheap. It gives you option of a 46 cassette, and will work properly. If you cannot afford this, go for the 28 chain ring, keep the 30 tooth and save for a 1x11.