Timber sash window recommendations?

[SarahG]

Just wondered if anyone can recommend a supplier for timber sash windows ideally with structural (rather than astragal) bar running down the middle.

 

Asking for a friend  

[Redbeard]

Do they have to be sliding sashes or would inward-opening mock sashes do? Do they need to be 'scrape-through-the-Regs' double-glazed or 'Fully Monty' triple?

[SarahG]

Sliding sashes with weights and cords and double glazed. Don't really want any mock features on the exterior as want it to look as traditional as possible. Thanks!