IMO
Buy a used bike that fits and is relatively inexpensive. Ride it until the wheels fall off and you lose a lot of weight. Treat yourself to a nice bike to go with your svelte form.
Or buy a used bike as above, Realize you don't really care to ride that much and you aren't losing the weight you hoped to lose. At least you're not out a lot of money and have something to ride when the mood strikes.
It is likely any bike made for your weight is going to cost a lot of money and will probably not work out in the long run as it is the wheels that take to most beating as they move far more than a frame does.
Good luck.