The cabin R-135 is in catagory 6A, that is the lowest deck( Riverea) outside cabin mid ship. You are in a great location. You are only a few steps from the elevator. The catagories are 4A-D, these are inside cabins, no window...then there are 6A-D which are outside cabins, the lower the letter the lower the deck. It doesnt really make any difference which deck you are on...the cabins are exactly the same. You just pay more the higher the deck. If you think you might get sea sick, then the lower the deck, midship is the best place to be. So you have a GREAT! cabin.
On the newer ships they also have catagories 8A-I and these are balcony cabins. There are also 5A cabins which are porthole cabins.
Hope this answers your questions.