Hi fkells,
There is another company called Sash Windows Ireland, which make traditional sash windows. As these are the real macoy, they are very pricey.
Have a look at the other threads on windows for information on various companies.
If you are still at planning stage you should choose your windows and then make the openings fit them rather than the other way around. This is because alot of suppliers have standard sizes, and you could end up paying nearly double for bespoke sizes.