be careful about buying something a size up and thinking it will make it look more modest. first this could make you look dumpy and draw attention to you. secondly when things do not fit properly it could make it lay wrong and actually leave you exposing more (such as sagging neck lines and sleeves or drooping pants - all could leave you exposed while you are none the wiser). if you are buying new stuff anyway find modest stuff that actually fits you well. you will look better feel better and if it is supposed to be covered it will likely stay covered.
Gap and Old navy are where I get most of my skirts. always simple, modest and inexpensive. also styleish. Honestly I never have trouble finding modest skirts. If you are looking to go more towards skirts but don't or can't shop[ it is easy to turn a baggy pair of jeans into a nice, cute modest skirt for just a couple of dollars. Also if you have some jeans a little past their prime (holes in immodest places) these are great because the skirt has a homey look that works well with little patchwork patches etc If you want instructions I can find some for you. I have step by step instructions with pictures on my desk top which is out of commission......
Old navy usually has some longer T-shirts/tank top which work great as layering peices. they cover my big butt. they are generally low cut but I put a top with a more modest neck line but that might be too short on top and let the tank cover the bottom.
Layering is your friend. your really really good friend.
a nice look that is in right now is dresses over jeans. My kids love tyhis style and I am more than happy to let them run with it. especially if they have a dress or skirt that has gotten to short, this is a great way to keep it modest and extend its life.
The truest answer to violence is love. The truest answer to death is life. The only prevention for violence is for the heart to have no violence within it. We cannot prevent evil through any system devised by mankind. But we can grapple with evil and defeat it, but only with love—real love.
(and i link my blog posts about this very topice)
if you had any intrest in seeing some more on teh topice of modesty
"Now bid me run, and I will strive with things impossible." (William Shakespeare -- Julius Caesar)