Meita: all I would say is, do the research. there is a lot of info on threads such as this, and on others in the vaccination section. the threads are long, but the info is there.
there are no tests, at the moment, to tell whether you are in an at risk group or not. some research suggests that if you/close family:
have allergies
have auto-immune conditions
history of vaccine reaction
history of autism
gastro-intestinal issues
then you might be wise to proceed with caution.
there is little doubt that the mmr is safe for the majority. no one has ever said it isn't.
but, on the other hand, it is not a vaccine with a good track record, imo (aside form vaccine damage). it was hastily introduced, and has been relentlessly pushed ever since - it has one of the worst safety records, overall, and has been through several different incarnations. the "recipe" if you like, is regularly tinkered with, and has been changed beyond all recognition form the early days - this without full trials etc.
the fertility issue wrt mumps is, as I understand it, a myth. there is a possibility of orchitis (rare) but to have double orchitis (I understand) would be astonishingly rare.
yes, you can get single jabs privately, althoguh no mumps anymore.
there is a book - by richard Halvorsen, the only nhs gp to offer both mmr and singles (and he has all the way along), called "the truth about vaccines". I found it an interesting read - it weighs up the risks, loks at the safety records etc, and lets you come to your own conclusion as to whether it is of benefit for you/your family. Richard Halvorsen also provides consultations via Babyjabs. afaik, he looks at each family on a case by case basis, takes history etc, and then advises accordingly.