As the socket 1151 is older, it supports 6th gen intel processors. To get these brand new would cost more for your money then it is worth spending. You should look into getting a new motherboard, CPU and ram but this will cost probably more then 200 euros.
What Motherboard and Ram do you have currently?
Is a 4 core Processor and 8gb ram good enough for you? as you may be able to get that for 200 euros.