if you want to have a gas fire, you need a Registered Gas Installer.
They are not usually keen on gas fires. Some are only qualified on boilers. Shops that sell gas fires usually employ or know one.
The chimney will need to be checked for size and free flow, and, if sooty, to be swept. Yours may not meet modern standards.
The fires with open gas coals are attractive, but very inefficient. The ones with a sealed glass window, the reverse.
If it is on the ground floor, you may be able to have one with a balanced flue through the wall instead of a chimney, it will need a sealed glass front.
You can also get some designed to resemble iron stoves that can look realistic.
There are some flueless gas fires, they vent the steam and fumes into the room so need extra ventilation. Many gasmen refuse to handle them, although the number of people and pets suffocated by the fumes in UK is quite small.