I just wanted to give a shout out to all that have helped with my research for Cornwall. I have now decided we will train to Truro from Bristol, picking up our car the next day. On the back end the same, train from Truro to Paddington station to catch the Heathrow express. Is the main station in Bristol called Bristol Temple Meads?
Yes, the City Centre station is Temple Meads. Bristol Parkway is out in the northern suburbs.
If your hotel is near one of the piers/ferry docks the fun way to Temple Meads from the hotel is on the Bristol Ferry waterbus.
Not many UK stations have a waterbus service!
Unless you have already bought Heathrow Express tickets at a discount (that needs to be done many months in advance) then you can take the Elizabeth line from Paddington to Heathrow. It's half the price, comfortable and rarely busy from Paddington during the day and only takes a few minutes less than the HEX.