If as you posted the house is 30 years old and has poor insulation, would there really be any point getting triple glazing if you were to lose most of your heat through poor insulation in your floor, walls and ceiling. Triple glazing is obviously more popular in Scandinavian homes, simply because the weather they get is much more extreme. If you consider newly built homes in Ireland built to the latest building regs, double glazing is more than enough considering our climate.
I suppose the point I'm trying to make is, whilst with triple glazing has the advantage of better insulation, consider how much more it could cost to maintain or replace in the event of damage. I'd be more inclined to go with the double glazing and sort out the other factors in the house that cause the house to be cold. Poor floor, wall, ceiling insulation, draughty door seals, letterbox, fireplace etc. What would be the point in triple glazing if all surrounding factors were leaking heat.