2 types of flooring my side extension - including original wood floors

This is proving the biggest decision-making question with my side extension build: we have great original wood flooring throughout my house - and now we will be building a side extension to create a big kitchen/diner at the back of the house and want to keep as much of the original flooring as possible. But that means that we will need to have two types flooring in the room. How difficult is it to run new flooring up against original floorboards? And has anyone done this recently? How does it look? Thanks!