Hi Ambie - have a wonderful time on yr cruise!! If you are cruising to Alaska, you will want the jeans. If you are going to the Caribbean, you will want a light pair of capris or shorts. It is blazing hot to walk around there!!!
I have been on 4 or 5 cruises. I too, didn't want to make a major investment in clothes. Even if I spent a lot of money - I still wouldn't like these clothes. (I'm now a tight size 20 but I was a 24/26 last cruise.) I was lucky to catch a couple of things at Marden's (kinda like Filene's Basement). I also bought a long black skirt on sale at Dress Barn Woman w/ stretchy waist that always fits & I take on every cruise for dress up.
I did bring a cuppla pair capris that were tight. I never wore them. They made me hot & sweaty. (They fit now

)
Some cruise ships have coin laundramats on board, which is good for me, since I don't have a lot of clothes. I have used their laundry service too, and find the price to be about the same as land based dry cleaners.
I normally don't get much exercise but on the cruise ship, I go the gym every day for 20 or 30 minutes because it's right there. It helps since I do eat more but I give myself permission!
I'm gonna chime in w/ everyone that it sounds a bit much to lose that in that period of time. And do bring comfortable clothes for all you shore excursions.
Happy Anniversary & make sure you tell us all about the cruise!!!