Undershirts

Today I noticed that I could see through my eldest daughter's shirt alittle bit. Not so much that I would call it see through but still. I found this kind of disturbing because I think that modesty is important no matter what age you are. This has me thinking about finding some undershirts for my little ladies to wear. The ones I saw at Target look much more like a negligee than I comfortable putting my small child in. I mean they look like something my DH would like to see me in after the girls are in bed! I considered buying an assortment of tank tops to put under the clothes but they are thicker than I'd like (so the outline would show under the clothes) and alittle more expensive. I'm hoping to find something more like onesies without the snap close bottom. Preferably some in short sleeves and some in tank top style. Does anyone have any suggestions? Does your child wear undershirts? All the time or just when a shirt is a bit tight or thin?