As the others have said, Janet, what was considered a good idea twenty or thirty years ago doesn't fit with the way we want to live today.
The "clever money" goes nowhere near them today, going instead for "garden rooms".
The difference being that a garden room is really a fully fledged extension with fully insulated walls and roof......... thus usable all the year around. You can imagine how much more expensive this option is though.
By all means go for a standard conservatory, but be resigned to use it only at certain times of the year. If you do, make sure you have a fully insulated door between the house and the conservatory or the heat losses from the house will be substantial.