Hi,
Your best option is to get a top-up mortgage from KBC. You will keep existing tracker for existing balance, and have a 2nd account with a different rate. Rate will be determined by your LTV, and you'll be able to overpay. Check details with them, but this is cheapest option.
Failing that, KBC are probably the cheapest personal loan rates. The interest rate is fixed for the term, but it'd be a shorter term than the mortgage option, and a higher rate.
Make sure you take advantage of the tax reliefs available under HRI scheme.