Sleestack - I've used mediums on all the OM's and 14 fret Triple O's I've owned, and I tune them to concert pitch. They work just fine, don't hurt the guitar and definitely give you a more powerful sound.
Something else you can do to increase the bass response is to put a John Pearse armrest on your guitar. This lifts your forearm off the top and substantially increases the amount of bass response that comes from the top.
Full disclosure: I am an artist endorser for John Pearse strings and accessories, but had John Pearse armrests on all my guitars long before I was given endorser status. What they do is allow the top to vibrate to its fullest. They make an audible difference in the tone of larger guitars, but on OM's and smaller body guitars they make a HUGE difference. The general rule is the smaller the guitar, the more impact the armrest has.
Here's a simple test you can use to tell whether an armrest will help you get the bass response you'd like: play a vigorous first position E chord with your forearm resting on the top. Then, while the chord is still ringing, lift your arm off.
If you can hear an audible change once your arm's off the top, and you LIKE that change, then you might want to consider getting an armrest.
Here's a picture of one on an OM:
That particular model armrest is called The Slimline, and it's the one I would select for an OM.
It's just a thought - as I wrote, I have them on all my guitars, and they really do what they're designed to do. Switching to medium gauge strings should also boost the bass response somewhat, but won't do it as dramatically as adding an armrest.
Armrests aren't for everyone, and there are those who absolutely despise the way they look. Naturally, they won't hesitate to share that opinion with you.
I use them for their indisputable tonal benefits: they really work. So it's a matter of personal preference - if you like or don't mind the look, if you put one on the guitar you'll get the tonal results that your post indicates that you want.
Hope this helps.
Wade Hampton Miller