Think about additional controls - zoning, programmable thermostats, loft insulation etc etc as well as the boiler.
Hoval are top notch boilers - not cheap but the dogs danglies and knock spots off the other brands. Would be my choice.
UltraOil® (50-80) | Hoval
You get what you pay for.
Looking at the 16/35
now THAT looks like a premium bit of kit