Believe me, nobody is going to see this as trivial. Because it's not. Feelings are feelings, and *nobody*, not you, me, your neighbor, priest or milkman can tell you that you should or shouldn't be having them. You just do.
PA (Physical Attractiveness) can be a powerful emotional need for some people.
I am guessing that really, at the deepest level, weight really isn't the issue. One obvious thing might be some kind of hormone issue after the pregnancy, perhaps things just haven't settled down yet, or perhaps post-partum depression or something like that. So I would encourage you to get that looked at to rule it out.
Other things it could be is that perhaps your wife's low self-image results from some need she has not being met. I coudln't say what it was, but I can offer a couple suggestions.
1) Go to the concepts link at the top, and print and read *everything* under it. These BC's (Basic Concepts" are the fundamental pillars on which MB is based. It is important that you have a detailed understanding of those in order to move forward.
2) Read several of the letters (pick any you want), in the Q&A section. Dr. H does a great job of showing how to apply MB principles in a real-world situation, where the application may not be quite as obvious. This will help you learn to apply the BC's to your own experience.
3) If your W is willing to explore healing the relationship, then in the Emotional Needs forum there is something called the EN questionnaire. Both of you fill it out,and then work on meeting the top needs of each other.
4) ALong with all this, Dr. H recommends spending 15 hours of undivided attention each week. That's not 15 hours of watching the tube, but 15 hours of *actively* spending time together. Spending time with your W will reaffirm to yoru W your desire to be with her, regardless of PA, and may begin to heal those wounds.
Getting over the porn issue is non-trivial as well. IN this case, it's a little like rebuilding trust. Can she trust that you're not judging her, or comparing her to all those pornstars. Dr. H has some good articles on recovering from infidelity, and part of that is rebuilding trust. While the infidelity part may not directly apply, the rebuildling trust part does.
Of course, your and your W communication must be free of LB's, DJ's, and all tha tother stuff, which you can learn much more about in the Concepts section.
I would encourage you to review all that material. Twice. Then see how you can start to apply it, and if you have other questions, don't hesitate to post again, somebody is always around that can offer some tips.
But a good understanding of BC is critical.
Good luck, let us know how it goes.