The balcony cabins on Baja Deck (and Aloha Deck too) are all identical; the only difference is location. If you have had no problems on the ocean in smaller ships you have nothing to worry about on a ship like Sapphire Princess; she is a very stable ride.
If you want a catagory BC cabin on Baja Deck you would need to book a specific cabin because there are BC cabins on Aloha Deck also and if you book a "Guaranteed" you could be assigned to either deck. Or you could save $50.00 pp by booking a Catagory BD on Baja Deck and you would know you'd be on Baja Deck as it is the only deck with BD balconies. But you don't save any more money by booking a Catagory BD "Guaranteed" so you might as well go ahead and pick your cabin. I would suggest one close to the forward or aft stairs/lifts, but not too close; somewhere around B240/B243 or B714/B715.
You will love Sapphire Princess; she is my favorite of the large ships--of course I say that about all of them. And she is scheduled for a refurbishment early next year so she will be sparkling when you go to Alaska.