Personally i wouldn't use copper, while it's perfectly legal to do so in the UK several other countries have banned its use for brake pipes and with good reason IMO. While it's not as "strong" as steel brake pipes the real issue is metal fatigue rather than outright strength i.e. it's more prone to failing where it's been bent on a tight radius or flared
Cunifer (aka kunifer, cuni, cupro-nickel etc) is what you want, it's a trade name* for a copper nickel alloy that's got amazing corrosion resistance, is nearly as easy to work with (bend/flare) as copper but with much better fatigue properties and similar to strength to the origional 'double wrapped' steel pipes... basically steel brake line is typically rolled from flat strip and brazed together (similar to rolling a fag). Cunifer (or copper) tube is extruded from a solid chunk i.e. seamless tube
Any decent motor factor should sell cunifer either instead of or alongside copper. It's not much more ££ than copper and waaaaaay cheaper than buying 1/2 finished (they need bending to fit) steel brake lines from MB
The one to watch out for is places getting "confused" and selling copper as cunifer, one of the giveaways is colour as cunifer is a lighter champagne/grey colour the other is the spec printed on the roll of pipe... if it says BS EN something or other C106 then it's commercially pure copper regardless of what it's being sold as
* named for the main alloying elements in it Cu Ni Fe r (copper, nickel, iron). Commonly/traditionally the material of choice for sea water pipelines and what Volvo used (dunno if they still are) for brake lines from the late '60s or early '70s
