If you are planning to change the whole layout, I would be inclined to position the kitchen along the full length of the left hand wall, with an island running parallel at the narrower end of the room. I would move the dining area to the opposite end of the room (where the window and door are). If money is no issue, replacing the window and door with bi-folds would add a great aspect to the room and connect your kitchen to your outdoor space.

You need all the dimensions ( including the cut out for the stairs and Hallway and the section of wall to the right by the entrance door.

However, I don't think an Island will fit and leave enough room for a dining table:-

I'd go with a peninsula arrangement, add in units to the right if they'll fit too. NO stools though!

The width of the room is about a metre too small for an island. I think the current layout works. Alternatively swap the kitchen to the front and put big doors at the back to the garden

If you are adding to what’s there - there looks to be scope for a small ( moveable ) chopping block type ‘island’ and a tall bank of storage / pantry /fridge run on the right .

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Would something like this be better? Like the above comments said you could swap the space around and put in a larger door to the back garden :-)

An island could work like this:

But personally I'd prefer a u-shaped kitchen on the toilet side of the room and a larg family dining table.

I personally would go for u- shape kitchen with a peninsula in the toilet end of the room.... have a wide French door put in instead of the window and door; but the star of your kitchen could be a big dining table by the new French door, looking out to the garden, as the heart of your home.
Ps: a floor to ceiling cupboard along the whole wall, top right hand corner of the plan, by the door, could provide you with crucial storage, a utility area or even a little hidden desk.

Thank you everyone for your input, certainly given me some ideas I hasn’t thought about. The annoying thing with the front is how low the window is, so limits some of my options. I’ve added a further picture to give some more context. And the area by the back door looks like it used to be a cupboard. Thanks again!