Without breaking the 6 hour flight rule, it's tough. Mexico or the Maldives would be amazing, but well over the limit.
I'd suggest looking at the Canary Islands. You get the guaranteed weather, and it's easy to avoid the touristy areas by picking one of the plentiful 5-star hotels around that tend to have massive resorts so you'd never need to leave. You can be pampered in luxury, eat the best grub or sunbathe to your heart's content, all without leaving the hotel.
Have a look on the usual travel sites (Expedia, Trip Advisor etc) and see if any of them take your fancy. Some of them look stunning, if you're prepared to give them a chance.