Ask around for personal recommendations of an experienced local carpenter. Properly done, there should be a substantial wooden trimmer across the joists to stiffen them and take the fixings, especially if one has been cut.
It should easily be finished within a day but some people will charge it as a day's work if they won't have time to get to another job afterwards. One person job.
Around £150 here but could be £200.
The wooden ladder that folds in half is more rigid in use than the lightweight aluminium ladders. Get one to suit your ceiling height. 2400 is common in modern or small houses, older houses may be 3m. Aluminium ones are more widely sold, cheaper, and lighter to carry out of the shop. Some have a sprung arm to help pull the ladder into place for stowage.
Grand houses with ceiling height exceeding 3m may need a special order ladder, and are harder to stow. It would be easier and cheaper to get an ordinary one-piece ladder of appropriate length and some kind of hooks at the top to keep it in place.
Have a couple of strong handholds at the top
Examples
www.wickes.co.uk/Products/Tools+Workwear/Ladders+Platforms/Loft-Ladders/c/1000447
www.screwfix.com/c/storage-ladders/loft-ladders/cat831470?cm_sp=managedredirect--storageladders--loftladders
If you are weedy, or not tall, or the ceiling is high, a light one is easier to push up and pull down, using a pole with a hook (provided)
Some come with a hatch, or the carpenter can make one and add architrave for neatness, and an edge strip to prevent draughts. Carpenters like making things out of wood.
if the hatch is separate and hinges down, I strongly recommend a Fanlight Catch that you can release with the pole. It is better than the flimsy touch latch usually supplied. You can get them in a silver finish off ebay which I think looks better than brass, or you could paint it white to match the ceiling (preferably before fitting).