Got my new conservatory done by a professional. Fortunately my neighbour is just that and he and his son did in an hour what would have taken me days!
They laid the self levelling screed one day, about 45 mins, and came back the next day to lay the Vinyl took them about an hour. Stuck down round the edges with spray adhesive and siliconed all round. He put me right on the correct type of vinyl. The ones for conservatories are more suitable for the greater range of temperatures encountered.
Get a quote from an internet company for the material then go to your local carpet shop show them the quote and tell them if they can come close to it they get the job.
This has two advantages 1) It helps keep a local trader in business. 2) You have someone local if things go wrong.
We did this with carpeting a living room, dining room, landing stairs and hall and the difference in price was not that great.
I always get the shop to fit - they have contractors on call for this - but even then things can go wrong. The last time they fitted a floor covering in a rental house I own, they left 2 small stones under the covering. As this floor cover was fully sealed at the edges, I am wondering what they will do. What I KNOW they will NOT do is charge me. The floor was laid less than 9 months ago.