Suvarnabhumi to Don Mueang Airport Transfer Guide
Luggage Storage, Delivery, and Exchange

Airport services may include luggage storage or delivery, which can help if you do not want to take a large bag on a domestic flight. The source mentions roughly 100 Thai Baht for a day of storage and about 299 Thai Baht for delivery, but fees and providers change. Confirm the current price, destination, insurance, and collection process before handing over a bag.
Cross-City Transfer from Suvarnabhumi to Don Mueang

A transfer between Bangkok’s two airports involves immigration, baggage, the city crossing, a rail or road connection, and check-in deadlines. The source attempted it with only a few hours and describes it as a risky challenge. For a real itinerary, allow several hours of buffer or consider booking flights from the same airport when possible.
If you have a connecting flight at Don Mueang Airport, the free shuttle leaves from Level 2, Gate 3. It is only for connecting passengers, and you must show onward-flight proof plus your passport or ID. The airport currently lists service from 5:00 a.m. to midnight every 30 minutes, but road travel time varies greatly, so leave a large buffer.
If you have a connecting flight at Suvarnabhumi Airport , there’s a free inter-airport shuttle from Terminal 1, level 1, gate 6 between 5 am and midnight. Show your onward ticket to board. Allow extra time during rush hour.
Rain Delays and Time Buffers

Heavy rain can delay taxis, buses, BTS, MRT, and airport rail connections. Leave early, monitor the route, and keep a backup plan. If your connection is tight, avoid adding optional shopping or banking errands between flights.
A Practical Airport-Day Itinerary

Finish essential arrival tasks first, confirm your luggage and flight requirements, then choose the most predictable route to the correct airport. Keep identification, cards, medication, and valuables with you. Prices for hotels, exchange rates, and transport in the source are dated observations, not current guarantees.