Evergreen hedge

I have been wishing my parents new house over Christmas and have got to talking to them about plans (they are starting to build a new house on the plot) for the garden. There are some existing hedges which are mainly hawthorn which need laying so that's a job for the next few weeks. 
There are also some hedges used for screening off which they'd like to make more private. From what I could see there was a selection of dogwood (different colours) the occasional birch tree and some other deciduous shrubby things in this screen they've inherited. It is patchy in parts and mum would like to fill it out with some evergreens to give it a bit more privacy during winter. She was originally considering filling the gaps with laurel but I thought it would look odd to have such informal hedging interspersed with laurel blocks. Does anyone have any suggestions for some evergreen interest which is quite informal? Or is it a case of rip it out and start again?