Hi,
I'm glad that your mw reassured you.
But for future reference, it is only when you have a really heavy bang/knock, or something sharp digs in a lot that you will need to worry. A cat jumping off you will not do anything to you or the baby. Baby is very well cushioned by the amniotic fluid.
This is baby no.4 for me, and with this and each of my 2 subsequent pregnancies I have always had a litttle one to look after - I have 3 kids aged 4 and under, and they are always climbing/jumping on me. I would only worry if I got a really sharp knock, or if they landed on my bump full on.
Try not to worry, I would think in a normal situation, you would only get such a knock if you fell down the stairs or had a similar sort of accident.
HTH
Heather x