So, you sound really thoughtful to me. I appreciate that. :>) Do you think that you may get more and more used to her body type the longer you are with her as you did with your ex? I think when we love someone, it can happen that we become more and more in love with them, their body, etc. But otherwise, you may have to make a choice. There is no right or wrong answer to this question, but how important is sex to you? For some, it's awesome, the most important thing and without a robust sex life, they couldn't be in a relationship. For others, safety, companionship and things like that are most important and not having the best sex life is acceptable because sex isn't the most important criteria. You have to judge where sex falls in terms of importance to you in a relationship. After more than two decades of marriage, long term relationships involve many aspects. People have to find what works for them. If you don't think you'd ever get to a place of being satisfied with her (and possibly then making her feel bad which isn't fair) and sex is of utmost importance to you, you'll possibly need to leave this relationship to find one that is better suited for you. Otherwise, you will need to focus on making your sex life with her the best it can be. Does that make sense?
So first, a couple of questions.
Are you sure you're over your ex? Are you ready to be with someone new?
I ask because you were with your ex for 10 years. She broke up with you, harshly, 7 months ago, and 2 months later, you have a new girlfriend. Maybe it's just too soon, even with therapy. That's okay - we all heal in our own time. I wonder if your new girlfriend had the same body type as your ex, would you be focusing on really different hair, or different hobbies, or something else?
To please any partner, ask what they like. It shouldn't be like a job interview, but while you're being intimate, you can ask what she wants you do to. Outside of the bedroom, ask her what her favorite things are, sexually. Ask if she has any turn offs. If you find yourself in a moment of hesitation, you can always stop intercourse, and maybe perform oral (if that's something you both like), or use your fingers, or something else you both like.
Ultimately, we like what we like. You just may need some time to get used to someone else, or this may be a body type you aren't attracted to. Time will tell, but in the meantime, remind yourself of the beauties of her body. None of us are perfect, but maybe she has gorgeous legs, or a really sexy back, or something.
If you find that you can't appreciate her body - which is okay - then she's not the one for you, and you should let her go gracefully and kindly.