Regardless of whether you buy a complete 1x crankset or just a chain ring, a 42t ring might work well, but not because it's the average of your two previous ones. If you need to (and it may be worth doing, to ensure you spend your next money only once), put it back to the 34-50 that it had and go ride your normal routes, looking for particularly fast and slow sections. You want to try to find the gear ratio range that works for you, on average. The shortest ratio (slowest speed) will probably be in your 34t ring. At your slowest, where are you on the cassette? Largest sprocket? Or do you never go that low? Maybe you go only as low as the 3rd largest or 4th largest. Say it's an 18t sprocket (for example). Whatever it is, that's your shortest ratio -- use a gear inches calculator (online) and find the gear inches. Say it's 35. Now figure your tallest ratio. Do you really need a 50-11 ratio? If you're up in the 50t ring, do you go as small as a 13t or a 12t or an 11t on the cassette? Whatever that is, that's your tallest ratio -- use a gear inches calculator to figure it out. Say it's 103.

Now you're armed with the data necessary to find what will suit you the best. If you're keeping your rear cassette, whatever it may be, start playing with gear inch calculators and determine what your range (shortest to tallest) will be with a 38t ring, a 40t ring, a 42t ring, etc. Maybe a 38t ring will give you a range from 32 to 87 (I have no idea what your cassette is, so this is just as an example). Maybe a 40t ring will give you a range from 36 to 93. Maybe a 42t ring will give you a range from 45 to 106.

You can see how, with the cassette kept as a constant, changing your single chain ring will move your range of available ratios up and down. If you find yourself more often using the shorter ratios, then you probably want to consider a smaller chain ring on the front. You'll lose top end, but you'll maintain your climbing gears. If you would rather have the top end and will walk the bike if forced to on a hill, then maybe you want a larger ring.

1x drivetrains are best served by wide ratio cassettes. Many run 42-11 cassettes or 48-11 or even wider. It takes more sprockets to keep the jumps reasonable. Lots to consider.

Good luck and have fun!