If you don't want to haul your luggage up and down stairs, don't take the metro. There will be stairs at some point at Gare de l'Est, and there will most likely be stairs also at your destination, whichever station it is.
Thanks, but I’m not sure buses and suitcases go well together. I may have to end up using a taxi.
If you have luggage, buses are much easier than the Metro.
And note that taking public transport of any sort with luggage marks you out as someone traveling with all his valuables; make sure you are pickpocket proof. I use a money belt under my clothes on this sort of transfer and then stow things in the hotel safe or apartment before venturing forth to explore. If you don't do that, at least make sure no wallets are in pockets or backpacks but are very well secured where no one can pilfer them. Pickpockets are highly skilled; you won't see them, the stuff will just be gone. And it goes without saying, never set down the computer bag or purse or other bag with the most important valuables -- not on the seat next to you, not at your feet.