Eterna les historiques1935 strap buckle suggestion

Mixing and matching colors and styles of straps with a watch is one of the fun parts of this hobby 😀

There are many, many threads on this forum that offer suggestions for color - it really depends on whether you like a formal, dressy look (black strap) or a more casual look (brown strap) for your tank. If you can't decide, look for a color on the dial that you might like to highlight - perhaps it's those gold-tone hour markers, or that unusual center minute track in black - and find a strap color that matches that color. You might like a strap in a yellow-tan color that enhances the color of those gold-tone hour markers.

As for taper, a tapered strap tends to look better on a thin wrist and is "vintage looking" which might be more appropriate for your style of watch. But nothing wrong with a full 20mm strap all the way around, something that makes more of a presence if you have thick wrists.

If you're still looking for inspiration, search for a vintage Eterna advertisement from the 1930s or 1940s and see what straps were used then. There are bespoke strap makers who will make you a vintage-style strap but upsized for a modern watch.