I'm surprised nobody mentioned a pretty obvious way out of the problem that wouldn't cost you anything. If you like the strings you have on the guitar, take off the treble E string and take it to a music store. Open a packet of the gauge strings you think you have and compare the high E in it to the one from your guitar. You may not think you could tell the difference, but when you lay them side by side .001 inch will be fairly easy to see.
I don't know what kind of resonator guitar you have, but my National came with instructions to use lights or mediums (12s or 13s, I assume). You also didn't say whether you play it in some slack tuning or conventionally. If you're playing bottleneck style in slack (open D, G, E6, C or something like that, I would recommend the heaviest string you can put on it without putting too much strain on the neck. If you're playing in standard tuning or tuned up to open E or open A, go for lighter strings.
I have run into some slide players who mix their gauges with heavier strings in the treble, especially the high E. Light strings in the treble tend to "bark" more; heavier strings will give you a throatier sound.