Window companies are usually good at fitting windows. If you want a conservatory I would recommend using a conservatory company.
I had mine built by Oakland Conservatories, and I cannot praise them enough. Â Their advice, pre sale, was excellent. The workmanship cannot be faulted, and everything was done as per the schedule.
Its no wonder that I have never heard anything but good reports about them. Call in at their small showroom for a chat about what you think you want, they are not pushy, or salesy, at all.