You can find kits on eBay for doing flex lines for T4 turbo feed and/or drain. These are very standard, easy to find and widely used. Here's just one example of a line and fittings. Going this route would eliminate one welded joint by replacing the entire turbo fitting with a made up one. Just search something like "T4 turbo oil line" on eBay for options.
You'll still need to braze a fitting on the other end. It would be something like this fitting I made up for my oil cooler lines when converting to AN fittings (note I ended up not using this setup, opting to modify the oil cooler and using a 90 fitting instead, but others have gone this exact route with great success)
Seems like -4 hose and fittings would work, but I think -6 would be what you would want to use if you decide to modify your existing hard lines.
Good luck