Even if you cannot make over payments you should look at a shorter term fixed and then every 2 or 3 years pay off a chunk before renewing at a smaller amount
Best advise I was ever given was to invest in bricks and mortar as most other things loose their value. We are on track to be mortgage free by the age of 45 with a house which will have cost us around £300k. The current value of our house is already £300k as it has risen by over 30% in 3 years...