The floor plan of your house reminds me of two crossed fingers, hope is a good omen, and you enjoy it!
I do not like to propose Ikea, I find it more appropriate to propose to the customer pieces a bit 'most sought (without necessarily spending a lot). Unfortunately I don't know the cost of a good London carpenter, so I'm not sure I stay on budget you set, for this reason, I kept ikea as a second option to create kitchen and closet of the guest room (thus remaining below the threshold that you defined)
