Downtown malls
A downtown mall half-day keeps one main hall. Go deep in Paragon and only cross the skywalk at CentralWorld, or the reverse. Pratunam and Platinum are the garment axis; if you want garments, replace the luxury day, do not hang them after Erawan as 'a bit more'. Jim Thompson is the indoor hour in the middle of a Siam day, not a third mall.
West bank and the weekend
The west bank and the weekend are two other corridors. ICON uses the Gold Line or a boat, on a different day from Siam. Chatuchak is the main stop only at the weekend; on a weekday JJ Mall's air-conditioning is not the market. Yaowarat's night street and Asiatique are one a night. All four corridors are listed so you pick one, not so you schedule them together.