Ground floor bedroom extension with skylights (Help!)

Good evening all!

I am new to this forum so apologies for my rambling!

We cannot afford a 2-storey side extension unfortunately so we are looking at a more affordable alternative.

This would be a ground floor side extension along with ensuite shower room/wc and a garage store to the front.

Because we have had to amend our dream layout, we are now having to compromise on having the 4th bedroom downstairs. It will have no windows apart from a couple of skylights on a vaulted ceiling.

My concerns are:
With it being a vaulted ceiling, will it meet building regs for fire safety (I'm hoping we can get some kind of opening skylights, to allow for ventilation and possibly escape in case of fire).

Major downside is that it will be difficult to access them easily as quite high up so not sure how to get around this.

Side windows are not an option due to neighbours next door, garage to one end and ensuite to the other.

We are desperate to make this work but any advice, info or recommendations would be much appreciated.

The bedroom will also coming off an open plan kitchen/diner (on diner side as it is L-shaped. Will the bedroom door need to be a firedoor?

Thanks in advance!

Kate