Without traffic the Conrad is 30 mins from BKK. On average it's about 45 mins to 1 hr, which already has a bit of traffic built in to that time.

I agree with the others in that your concerns are overblown, it would have to be a pretty epic traffic meltdown for it to take you hours to get to the Conrad.

(In 40ish trips to Bangkok over the past 15 years that happened to me exactly 1 time, took 2 hours from BKK, that was arriving at 10am during a Thai holiday.)

From BKK>Conrad I always take the AOT car service, it's 1200 THB for a nice clean small SUV. There are multiple AOT desks inside baggage claim and just outside. They take cards, you go outside (on the same level as you exit baggage claim), give the guy your slip and your car will pull up 2 or 3 mins later.