We recently broke from a 1.95% fixed rate with Avant for 7 years (had fixed in February 2022) to a 2.5% rate with Avant for 22 years. There was no break fee. Time will tell if that was the correct strategy however we wanted the security of knowing how much we would pay each month until the term end and we have no intention of ever moving house. However since you are looking for a top up in a few years time, fixing for a very long period like we did may not be good for you...