How small is small? And what do you consider essential appliances? Apart from fridge, cooker, sink?

This is a helpful podcast if you are thinking about what size of kitchen island you want or what to go for: https://shows.acast.com/love-your-kitchen/episodes/exploring-function-over-aesthetics-with-amnda-hughes

One option could be to make the sitting room bigger, than you have drawn, to fit a large sofa and creat a corridor behind the stairs with cloaks cupboard, then the kitchen on the left with island peninsular facing the garden and the extensions forming the dining/seating areas

once you draw it to scale and position the kitchen and island there isn't enough space for a sitting area ( where you have dining) also it would be too tight to have the sitting area where the kitchen is on the plans. you need walking round space and you would have to have a sofa that is max 2,5 m wide and it would still feel a bit tight. I have actually tested it. Since a first glance yes the idea of a kitchen island looks good. But when you put everything in, you see that it just doesn't work well. I used to be a kitchen designer back in the day and I always hated that most designers didn't consider all elements of the space and how everything works together, but only cared that the kitchen is as big as possible since they get paid commission on the % of the price. Just in case if the kitchen designer was trying to convince you to have the kitchen there with big island. you could have a peninsula if you wanted I don't see an issue with that. If you want send me a DM and I can schedule a complementary 30 min zoom and show you in 3d what do I mean.