Well, you definitely shouldn't stay on variable. You're paying 630 a year in interest that you don't need to (90k * 0.7%)
So, the question is how long to fix for.
I normally say fix for as long as you can, but in your circumstances where you've a plan to sell in maybe 3 years, then fix for 3 years.
If you fix for 5, and break in 3, how bad could break fee be? If interbank rates remain as they are you're looking at maybe 400. If rates go up, maybe zero. I can't see a situation where rates fall but it could happen and push up a break fee. But you're looking at an extreme scenssce where it's more than you'll have saved in interest.
I'd say fix for 3 years, keep under review and reassess each year to see if your outlook changes.