I have a Rad Power Bikes Mini Step-Thru 2, with a seat-top height of 35" from the ground, and that's with a thick Cloud 9 cruiser seat and Redshift suspension seatpost. Even so, I could drop it to 32" if I had to (I just rechecked it with a measuring tape), and in stock configuration (regular seatpost, thinner seat) it should be good down to about 29". Plan on upgrading to a thicker, more comfortable seat, though, but 30" should still be easily doable even then.
And yes, it can be folded. My knees and I love mine. Note that, on their website's bike-geometry page, the seat-height dimensions are measured to the bottom of the pedal stroke, not the ground. If you decide to buy a Rad bike, and know anybody with one, ask them for a referral code to get $50 discount.
I've never heard of GreenBike, but just checked it out quickly, and it looks like they make a folding step-through version of the bike you already have, so you should check that out as well. Maybe they take trade-ins.
Our electric folding bikes store easily for travel or small spaces, fit a range of rider heights, and are ideal for apartments, condos, RVs and more.
www.radpowerbikes.com