If you’re arriving very early in the morning, the malls may not be open yet, and I don’t think they have a sort of concierge luggage storage if that’s what you’re looking for. There’s lots of luggage storage right around Terminal 21, though, including lockers right at the BTS stop. You can also use Airbnb to search for
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luggage storage now (they partnered with Bounce, and I think you get a discount if you book through Airbnb, but you could also go directly to Bounce).