Hi blarney ,
In the exact same boat as yerself..lodouble bed size base for old bed frame with those 2 metal bars ..thinking of going to IKEA in belfast.
For doubles though the width is an extra 5mm and the length is extra 10mm...For the SULTAN LOVANE base they have, it looks like you can hack a bit off at each end!!2.5m at each side ight be easy to overcome if you put a few planks under them...
Come to think of it IKEA will be open here in July so if you hang out till then they might have bed bases in Irish sizes...
I remember in an old house I rented they had a wooden base with horse hair on top and all covered in a material...I think this is exactly what I would need but doubt they sell them anymore...and I sure as hell wouldn't buy one second hand..