Bad luck, Freddy - especially at this time.
WB boilers, although dearer than most, are usually considered reliable and longish-lasting but I suppose it had to fail sometime. I don't know what model you have but I think a replacement heat exchanger can be bought for under £200, and even with fitting costs would likely give you back your boiler for much less than any complete replacement - assuming the existing boiler is not otherwise potentially cream-crackered. I would caution against buying any used boiler (complete) unless it is very new and has only recently been de-commissioned; I understand that boilers can deteriorate quite rapidly during storage out-of-use.
PM me if you want to run any ideas for the repair/replacement past me. Meanwhile, snuggle up under a warm duvet, woman or both - and leggings and thigh-boots will help too.