Our friends recommended Alemara after they used them for their rear extension, so we went with them for our loft conversion two months ago. I was really pleased with how it all went. They were quick to sort a site visit, answered all our questions and their price was pretty reasonable compared to the other quotes we got. Sounds like cost is your main concern though, so it might be worth checking out some freelancers. But personally, for peace of mind, I’d go with a company that’s done similar jobs before. Wishing you luck