A while ago, I build my in-law (75+ year old, 4' 8", 142cm) a 15" step-thru aluminum frame road/hybrid $80 on eBay.
Only 17" frames are available now:
https://www.ebay.com/itm/392817866782
I put 24" rear wheel with disc brake, 650 front wheel with light carbon fork, 148mm crankset.
2x8 drivetrain. Under 20 lb. (9 kg.) even with kickstand.