Water based sealers are not as effective as solvent based sealers. In order to get the protection you are looking for, your going to have to suck in some fumes. I would take the precaution of keeping pets and kids away while your laying down the sealer. It is going to be difficult to find an eco-friendly sealer with the protection you desire.

Look into Sealer #1 from Stone Technologies....might be what you are looking for.
* Wear a mask

Klet, thanks. That's what I figured. However, having had time to reflect I've decided because of on-going lung problems and scaring, I'd bettr stay away from the solvents. So I'll have to make do with water-based. But I'm going to keep a little journal to post and will note for the benefit of others this good advice.

I'm hoping this really looks good when done, and might be of use. Even if it isn't as nice as I expect, someone may getter a better idea (and most anyone could probably be a better craftsman).

If there is anyone following my project through the months, FYI I've about got the garden shape formed, have covered the proposed patio area with newspaper and weed fabric after spraying it with Roundup, and will be covering that with pinestraw for the summer. I'll spend the summer triming stone ends, carefully sorting pieces by width, and using color enhancing sealer. Should be ready to do the dirty work when it cools off in October. (Coastal South Carolina is the land of milk and honey, but the summer could kill a guy doing this kind of work.)
David