Here in Portugal you can't get laundry borax no way, no how. However I am able to get from a chemical supplier the following products.

Sodium Borate (granulated for agriculture) (# BORATO DE SÓDIO (Granulado Agricultura))
Anhydrous(?) Sodium Borate (# BORATO DE SÓDIO ANIDRO)
Granulated Decahydrated(?) Sodium Borate (# BORATO DE SÓDIO DECAHIDRATADO (Granulado))
Powdered Decahydrated(?) Sodium Borate(# BORATO DE SÓDIO DECAHIDRATADO - PÓ)
Sodium Borate pentahydrate (# BORATO DE SÓDIO PENTAHIDRATADO)
Granulated Boric acid (ÁCIDO BÓRICO - Granulado)
Some other form of Boric acid (ÁCIDO BÓRICO - PALHETAS)
Boric acid in powder (ÁCIDO BÓRICO - PÓ)

Anyone have any idea which is the most suitable?

Thanks in advance.

Borax is sodium tetraborate decahydrate, which is sometimes also called sodium borate. If you are using borax to raise the PH, then this is the way to go. Sodium Borate Pentahydrate will also work. It is essentially the same, but more effective per unit weight.

If you are using borax to add borates to the water, then you might want to use Boric Acid instead. Boric acid contains borates and lowers the PH ever so slightly. That means you don't need to use large amounts of acid when raising the borate level.

Haha, you've answered (extremely quickly) the two questions I should have asked ! Thanks Jason