Your mom is just desperate for you to have children and to satisfy the fact that you have somebody. Honestly never settle. You settle because you do love that person regardless of your wants. Because I always say this: What you want isn't going to be what you need and what you isn't always going to be what you want. What do you NEED in a woman? Then figure out if your wants compliments or clashes with your needs. Chose whats best for you, not what your mother thinks. Because she sounds like she doesn't have the wisdom to even tell you that.
If you don't feel you want to settle for someone like that, then don't. Don't try and force it to happen if you know that's not what you truly want and won't truly make you happy. What are you exactly willing to do? Listen and trust your own instincts or just follow and do exactly as your mother expects you to?
You don't have to settle for anyone. Now, I don't want you to think I am criticizing you, I am not. But it's not necessarily bad to like fat women or fat people in general. Fat people need love too. And there are plenty of people who are divorced or widowed who would make amazing partners.
But if you want to be with someone you are happy with, then you have to choose someone you are interested in. I don't think it's right for your mom to try and bug you into settling. That's the worst thing you could do. Because your whole life you will be wondering "what if".
Just gently explain to your mom that you will settle when you are ready (and if you are ready!), and that she will be the first to know when you have met that special person.
If she brings it up again, be firm. And remind her what you said before.
Nosey questions like that are the worst. I'm at the age where I am getting them now. Just be firm and let your mom know your wishes for your life.
I'm 35 and I don't settle for something, there's no reason you should. Find someone that makes you happy, they are out there. They won't knock on your door so you need to do a little foot work, but it will happen.