Hi Brett,
Welcome to GTPopping.com!
Day trips can be a little more difficult to source given the specialist nature of the pursuit.
Fiji would possibly present your best and most cost-effective option for you. A popular holiday destination for those with partners, safe, plenty of flight and hotel special and there are a couple operators both on the mainland and on Kadavu to the south.
Bali would probably be the next option after that.
There's been quite a few members on here that would have done exactly what you are looking to do and can elaborate on both destinations for you.
Luke