Fixing depends on your circumstances. If your mortgage is 30% of net income then a 100bp increase in rates will hurt a bit, and 200bps will hurt a lot.
Personally I think we are at a point where retail mortgage rates are going to start rising very soon in line with what wholesale rates have been doing. Avant started already last week. I fixed for three years with my provider in January, with hindsight I probably should have fixed for five years. In your circumstances I doubt you will have regrets fixing for five years right now.