I would have been better off in a dress shirt with long sleeves.
この場合、次のような言い方ができます。
ーI should have worn a long sleeve dress shirt.
「長袖のYシャツを着れば良かった」
should have ... で「…すべきだった」
ーI would have been better off in a dress shirt with long sleeves.
「長袖のYシャツの方が良かったな」
would have been better off ... で「…の方が良かったな」
ご参考まで!
A long-sleeve dress shirt would have been fine too.
A long-sleeve dress shirt would have been fine too. 「長袖のドレスシャツでもよかった。」
"long-sleeve" は「長袖の」を意味し、"dress shirt" は「Yシャツ」を表します。"would have been fine too" は「~でもよかった」を意味します。
他の表現として:
It would have been okay to wear a long-sleeve shirt. 「長袖のシャツを着てもよかった。」
具体的な例文として: Although I wore a short-sleeve dress shirt, it was cool enough that a long-sleeve shirt would have been fine. 「半袖のYシャツを着ていたけど、涼しかったので長袖のシャツでもよかった。」