You need to research the steel (not aluminium) window manufacturers in your area. As steel is stronger than timber and aluminium you can use a smaller cross-section for the door frame to get the slim line look. However steel framed windows and doors do transmit temperature as metals conduct heat well. Beautiful and expensive, but not thermally efficient.

https://www.steelwindowdesign.com.au/projectgallery#/private-residence-in-toorak/

Best of luck,

Dr Retro

of Dr Retro House Calls