I could recommend the company Speidel to you. We also visited Fermo, but the price was completely off. However, the price alone is not decisive; in the end, it is the entire construction performance and the possibility to incorporate your wishes. We are currently building with Speidel, and after some skepticism, I was truly proven wrong. I can only advise against a prefabricated house, no matter which manufacturer. Prefabricated houses are currently being built around me, and when I see the substance, I can only shake my head. You spend hundreds of thousands on chipboard and insulation, with a few wooden beams in between. Ultimately, a prefabricated house with interior finishing only takes 4 weeks less than a solid house, but of course, you are not told that in Fellbach.
Build a solid house with a basement and ideally monolithic without Styrofoam on the walls. This is very easy to plan and much better to design than the cardboard and gypsum board building kits.
The trades at Speidel are from the region, all down-to-earth and mostly family businesses spanning generations. I am very happy with the decision and would decide the same way anytime. So far, I am very satisfied with the execution and quality. I go to the construction site every day and am therefore always up to date.
Best regards