We had a very high nuchal (5mm) and, although it turned out not to be one of the three most common trisomies, it did turn out to be another problem - a very rare genetic disorder and we terminated at 30 weeks, which was extremely traumatic.
I did a lot of reading about high NTs at the time and, with an NT of 5mm, the chances of a completely healthy baby are about 50%. For an NT of 7mm, the chances are lower and odds are that, even if your baby does not have Downs, they have something else.
For us, waiting and having follow-up scans, etc, was all very stressful. We did it because we really really wanted the pregnancy to be successful because it was the result of extensive fertility treatment and years of waiting. To be honest (and I realise this is mostly coming from a very pessimistic place - I terminated only a few weeks ago), if you conceived fairly easily and naturally, I think you would probably find it less stressful overall to terminate now when it is physically much more straightforward than to continue the pregnancy when there is such a high chance that there is something wrong with your baby.
However, you should also consider having the Harmony blood test done, as the CVS isn't an option for you - it is expensive and only tests for Downs, trisomy 18 and trisomy 13 but it would at least tell you whether one of those is the issue.