If you really want spares, I think you can get some eggs frozen for possible later use.
(Right?)
I, too, have only one ovary, having lost one–and the corresponding tube–in 1992 to a ruptured ectopic pregnancy.
I had a daughter in 1995 (8 lb, 15.5 oz).
I had a son in 2000 (12 lb, 2.25 oz).
I had a daughter in 2002 (10 lb, 4 oz).
I guarantee that you can be as fertile with one ovary as you can with two!
(On a side note, all my kids were delivered via C-section–note the birthweights. I told the doctor that I wanted a tubal ligation performed as soon as my third child was born (to avoid an extra surgery, you see). This he did–and now I refer to it as having had my tube tied! 
)