Maintainers are awesome yes? I learned alot from them when I was a scrawny 119 lbs (not good).
There will always be folks who think you are too thin. They will comment and I will listen. I am effected by what folks say. We're human, you and I ...tsk!
You and only you can decide what you want to look and feel like. You aren't 6 feet tall are you?
Don't dispair about sizes. They make small stuff. I asked gals, who are smaller than me, where they bought uniforms. Some xsmalls are smaller than others and some companies make xxsmalls.
Shop. That was hard for me to start doing. Where the heck do you go if you don't know what size you wear? You just keep trying. My favourite dress pants are a girls size.
Coming to 3FC really helps me to keep my head on straight. I highly recommend it.