Hippie lawn

I once saw an article that referred to some ground cover that is super comfortable to nap on. It had a picture of young lady, in hippie-type attire, sleeping peacefully on it with her face pressed against the greenery.

I vaguely recall the article referring to the plant as a "hippie lawn."

Any idea what it might have been?

some totally wild guesses, based on plants people sometimes use for this and my own efforts to make a diverse yarden, good for walking on, hanging out on, maybe some edibility, but without grass-

chamomile, or its wild cousin - pineapple weed
sweet wild violets or its more tame cousin viola, aka heartsease
of course theres always permie favorite - clover, of many types
self heal is good for this purpose
as are all mints

ah theres more...but my first guess would still be chamomile or pineapple weed as the one you are looking for. mostly because it is more commonly known about as an alternative to lawn.

creeping thyme perhaps.

It was probably Roman (perennial type) Chamomile. I'm trying to start a chamomile lawn with it now. I got the seed here:
https://www.horizonherbs.com/product.asp?specific=941
This was the picture from their advertising:

I have long understood that the best chamomile lawns are made from a non-flowering variety (e.g. Treneague) so you would need to grow them from division, not seed. Not that seed won't work, just be a different sort of lawn!

I agree about the nonflowering type being the best for lawns, at least in areas where lots of kids play barefoot. We had flowering R. Cham. as part of our lawn mix, which attracted a lot of bees. Great to attract the bees but it made walking across the lawn similar to walking through minefields.

It was probably Roman (perennial type) Chamomile.

Also known as English Chamomile. (It was introduced during the Roman conquest.)
It is a low growing ground cover, and grows best when 'trod upon' according to Shakespeare.

It can be used for a tea, but the German Chamomile is the one used mostly for that -
- the two are not even remotely related, except by name.

Well they are at least in the same family, unlike for example Saxifrage and Burnet Saxifrage. Just goes to show how confusing common names can be.

Anyway, I was going to put a vote in for Yarrow (OK, Alchemilla millefolium) as a non-cutting lawn. Its got lovely soft feathery leaves, a mild scent and edible as well. Quite often grows in lawns anyway, but I don't think I've ever seen it grown deliberately as a monoculture for that purpose.