If you need to know that your repayments won't go up, then a fixed rate might be good for you. But again, as you point out you'll miss out on any decreases.......
If the past few months has shown anything, with so many people ****ed off about their fixed rate mortgage, it's that you need to think about what would be the better outcome for you.
For example, if rates rise & your mortgage repayments increase, would that be worse than if rates fell & you missed out on any decreases.
Other things to consider, rates are very low already - no-one knows how much lower they will go. Also, even is you get a stndard variable rate, there's no guarantee you'll get decreases passed on.
It also depends on the difference between the fixed & SVR you've been offered.