responsive design theme without featured images

I’m considering moving to a responsive design template. I’ve tested quite a few, the problem is that all my images are gone on the index page. It seems they all require images to be “featured images” to appear on the the index page. The previous templates I’ve used didn’t require that, so as I want a responsive design template with images on the index page, I have 2 options.

– Modifying all my posts (800 of them) to replace the standard image with a featured image.
– Making a child theme from a responsive existing theme to accept resizing images which aren’t featured.

I’m weighing the 2 options, and I’ll gladly accept suggestions.