Cheers, it really depends on u. Your Oscar results is v good. But it is still a probability test only and not 100%, so if u are the type cannot take any risk at all given your family history, u may wan to consider amnio. If not for your family history I would say your Oscar result is v good. My gynae recommends gynae for risks worse than 1:300 generally so your result is v good. Only thing is your fear due to family history.
I just did my amnio a few days ago due to not so good oscar though no family history, previous bb ok etc. But because we are very clear the outcome will affect our decision we went ahead with amnio. It carries a small risk of miscarriage but most Gynaes will assure it is actually v safe most times.
At the end of it, u and your hubby will need to decide for yourselves whether you need 100% confirmation. Having said dat, amnio also only tests for genetic probs such as DS. There are still other probs that can only b detected later such as detailed scan and some that will not be picked up even at detailed scan.