Sweetie - that is SO BEAUTIFUL! And don't listen to anyone that told you that tattoos are trashy. I agree that some women or men seem to have too many and it can make all of the tattoos loose meaning etc, and CAN look trashy but not knowing you and what you have already - you can't say that getting one tattoo will make you look trashy.
My sister would NEVER get a tattoo on herself but she NEVER thinks I look trashy with my two as mine tasteful and have a deep personal reason behind them. For example, I have a beautiful detailed celtic cross on my lower back to represent my celtic heritage, and the L in the center is the initial for my twin sister's first name.
That angel is beautiful and having lost a baby myself, I can understand why you would want to record it in a tattoo.
Another lady here mentioned that maybe you might get a lot of questions about it if you put it behind your neck for all to see - so I agree that that is one thing you should think about before putting it there above all other parts of your body. DO you want to be asked all the time what the tattoo means? If you don't mind talking about your baby then go ahead, but if you don't think you could bring it up all the time, maybe a shoulder or lower back, under belly button etc is best.
Just something for you to think about! I say go for the tattoo - but just think about how visable you want it to be once it is done for your grieving process and future questions.
1 Miscarriage myself, 13 Weeks 2 Days Pregnant with #1