I tried searching for one, and I did come up with this...
That's not quite the design I had in mind, and it's way pricier than I had in mind, as well.
I was picturing a 4"x4" cut in half and used as the 2 sets of lateral legs. Then a 2"x4" connecting the split 4"x4"s in their middles, as the "hip", and some 2"x4"s coming up on each ends, to make the support for the hammock suspension.
Voila... Just set baby in as if he were using it as a chair
My idea is to make this thing kinda tight, because I'm thinking that the less sag, the more rock the baby will get when it kicks. The shorter the 2"x4"s on the ends, the less chance the baby will have a hard fall?? And, of course, less torque on the ends.
Doubtful, tho... because I'm gonna need to come up with some walls. But that's what I'm really here for. I was thinking about styrofoam with slits so that you could just pop 'em on the right & left sides of the baby. Have some pins to hold the sheet in place, inside the sheets?!
But I think a better idea is to have a secondary sheet on the sides, that hangs closer to the center of an amsteel ridgeline. I got that idea at looking from the link above.
Think it might work? Or will you all discourage me?
And, of course, I'm sure these parents won't let their infants sleep without adult supervision. At least not at first.