Most people buying a home plan to sell it at some point. A non-conformist home is going to be harder to sell later, so it's harder to sell now.

You're unlikely to get something how you want it, unless it's built for you (and even then). You're probably going to need to find something with the outside you want, and budget to put the inside you want too.

But more specifically, an Eichler simply isn't going to have insulation and continue to be an Eichler. They're designed for a climate which doesn't need insulation, and as such, there is no room for insulation (at least for the ceiling). Try to find one with a big tree on the south side, shading the house (but make sure the tree is in good shape).