As you are second time buyers, you will need a deposit of 20%. So if you are planning to spend €200k on a house, you will need €40k. While lenders can make exceptions, I doubt if they would make an exception for you as you already have a €200k mortgage.
You have a very cheap tracker mortgage, so your costs of accommodation are very low. Most of your repayments are capital. In other words, you are quickly building up equity.
I would say that you have to be thinking medium term - at least three years away.
In the meantime, build up your cash reserves. It's possible that BoSI might offer borrowers with trackers a deal to refinance their trackers. For example, if they were to offer a 20% discount, then you would suddenly have a €40,000 deposit.
Brendan