Platinum or gold? Gold is the classic but pure 24 carat gold is too soft so go for 18 which is around 75% pure.
White gold is 75% pure with other lighter coloured metals added. It’s then rhodium plated which will wear off over time and need re-doing.
Platinum is heavier and harder so won’t scratch as easily. Its more expensive though.
Style wise, I think a plain band looks best. Flat on the outside or rounded, select anything from 4mm to 8mm wide depending on how big your hands are and how much you love bling.
Does your ring have to match your wife’s? It is nice if it does but not essential.