Hi
@Joeycreature and welcome to cyclechat
My fiancee' took to cycling when she was 18 stone and she's about 5'2". So don't let your weight stop you. It matters not a jot.
Obese? You mean
voluptuous yes?
That's the term my partner and I use anyhoo.
Any cyclist will happily admit that their first couple rides after a long time away from the saddle will have been less than speedy and quite short. Feeling like dying as you get to the front door is perfectly normal. It does get easier over time. No doubt you already know it'll be a while before you pose any risk to competitors in the Tour deFrance.
Decathlon has been mentioned already and whilst I won't go as far as saying this is the bike for you, it does seem to me at least, the way to go.
A mountain bike.
Will you be traversing up the side of Everest? Possibly not, but hear me out...
It's sized (small, as far as I can tell) perfectly for you.
Mountain bikes naturally have pretty low gears which will help lots as you get fitter. It's not the number of gears that makes a difference, but the size of them.
Please don't take this the wrong way, but mountain bikes are built for strength so it'll do better at taking your weight.
It'll take a rack on the back for carrying a bag with energy enhancing food like chocolate, sweets, cake etc
Mudguards will easily fit if you want them.
And best of all, a mountain bike will happily take slick tyres, which are a bit faster to ride on than knobbly ones. Contrary to popular belief, slick tyre cope very well on offroad surfaces...except for when it gets really really slippy. The mechanic (and I use that word loosely) will no doubt swap the tyres over if you ask when buying.
One last thing which I think bothers every person who ever bought a bike is that the saddle may or may not suit you. Perfectly normal and you might go through a few before finding one that you're comfy on. Or you could be lucky and find the one supplied perfectly ok for you.
One last word. As much as many of us here would agree that buying a cheap (under £250) bike probably isn't a good idea as the parts they're built with are usually rubbish, I wouldn't go spending a fortune yet either. The reason being that bikes depreciate quickly in value and if you don't take to cycling like a duck to water, it could be a costly mistake.
I really hope you enjoy it though. It's the best