The main factor is lighting, not a magic film stock or camera setting. That look comes from backlighting the subject with the low sun, then adding fill from the camera side so the face and body aren’t lost in shadow. The fill could be a large reflector, gelled flash, or both.

Why yours looks muddy: if you only expose for the bright backlight, the subject goes too dark. Trying to lift those shadows later usually just gives muddy results.

Helpful approach:

• Shoot when the sun is low for the warm glow and less intense contrast.
• Meter carefully; accurate metering is important for film.
• Add front fill with a reflector or flash to balance the backlight.
• A larger negative can also help give a cleaner look if you’re shooting medium format.

For film, the answers suggest Kodak Portra rather than Ektar for portraits, since Ektar can render skin too red. Portra 400 would be a reasonable choice here.

So: use low-angle sun, meter accurately, and most importantly add fill light to the subject.