Awww, don't feel like a bad mommy--you're not. You are trying to make the best decision for your little one, nothing bad about that.
I posted this in an earlier thread, but the advice is the same..
First off, I would not recommend an immediate switch after you bring your little one home. (Switching food cold turkey can often cause digestive upset. ) Instead, switch gradually.
As far as finding the 'best food possible', you will just have to try out different things and see what is the best match for YOUR little one. All dogs are different and what may work for one many not be the best for yours.
Research brands now, gather info on pet nutrition and decide which brands you think would be worth a try. dogfoodanalysis.com is a great source for info regarding ingredients in commercial foods, but keep in mind it and the ratings system were written based solely on the opinion of the site editor(s), not long term professional research. You have already been given some great resources to help you out, but here are a few more that will compare brands, home cooking, supplementing and that will give you some pretty in depth info on nutrition.
Dog Food Review Ratings
The Dog Food Project - How does your Dog Food Brand compare?
(I personally LOVE the second site...it examines some of the commonly preached inaccuracies regarding "taboo" ingredients.)
Good luck!