I know you don't want to buy online, but if you buy from a local brand (John Lewis) online you should be able to return it to the store if you don't like it. I usually like to try on in person as well, but sometimes it does pay to shop online. I also shop Ebay for brands that I know fit me well, some excellent bargains to be had.
I am confident that prices will go up, but having said that.....this is a vacation and since you need to take this week, just pay it and negotiate later. When prices dropped considerably after final payment for a cruise I booked, I used that as a bargaining chip to negotiate a better cabin. Don't stress over NCL's nickel and dime push, plan what you think is reasonable to spend for the experience you want and let it ride. Good luck