Previous car used to get through headlight bulbs - not quite as quick as yours, but never lasted a year. Then I decided to give up on the Halfords own brand, and go for the Bosch ones. 1) They were brighter, 2) They were still shining just as brightly when I sold the car two years later. I understand that Philips headlights last pretty well also.
On acquiring the 159 its (factory original) lights were distinctly dim, so all 4 bulbs replaced with Bosch Pure Light H7s. I'm hoping the main beams will last a good few years, as they are quite tricky to fit. If I do ever need to replace them, it will be with Longlife bulbs. Dipped beams are plenty bright enough, but I might go for the 2 for 1 offer on Bosch Plus 90, to keep for when a dipped beam goes (lights are on for ~60% of driving).
Possible electrical issue, but what it also could be is worn shock absorbers causing the bulb filaments to vibrate a lot more than they are designed to do, making them fail prematurely through mechanical wear.
Didn't realise the upgraded bulbs had a shorter life until the other week when the Osram Nightbreakers went after just 12 months in my wife's 159. I bought some Philips 130%+, read the package and then saw the honest appraisal that showed their performance as being much better than standard bulbs in all areas except average lifespan. Thought we had a problem at first