Dont take this wrong way or anything but . . .
If your fat or generaly sightly bigger in build buckets can be alittle bit narrow and uncomfortable - depending on brand as some are wider than others and more padded in different areas depending on style.
If you can get to somewhere like Demon-Tweeks or any similiar larger aftermarket supplier they will have seats out for you to try and sit in. Even some larger Halfords/Ripspeeds have buckets on site for you to sit in.
Best thing is to sit in one have a wiggle about and see what you think before parting with your cash.
Like also mentioned if you want to still carry passangers in the rear your be wanting non-fixed chairs but if not go for fixed. Also most buckets are designed to used along with harnesses so dont foregt to budget for them as well