Thanks for the comment. It is good to know that it'd cost a lot more if I were to book a room on Lido now. I haven't had motion sickness for long time. Hopefully, the ocean will be kind when we cruise this summer.
As why we made a 'guaranteed' reservation, well, that is because we booked pretty late and there were not many rooms left. Also the travel agent said the best option is to take a chance. So we did.
In fact, like you said, there isn't hardly any mid-ship room at this point so we'll keep the room they assigned. Thanks for your help!