As with most things in life the options depend on what you want to spend. At the top end a cruise on QM2 to New York and then to New England would be something very special - especially around September when the autumn colours would be still resplendent. Another top end cruise line to consider is Celebrity which is more reasonable but still upholds good cruise traditions if that is what you are wanting eg dressing for dinner, good range of entertainment etc. Some other lines such as NCL make more of a virtue of a more free and easy approach - so again it is another point to consider.
Try something closer to home plenty of ships going south that time loads from P&O who are not bad RCI their new ship is getting very good reviews or maybe a short flight and try a Celebrity cruise from say Rome,but Having done a New England cruise it is well worth it get your self a specialist cruise agent discuss your requirements with them they should be able to recommend a cruise Best of luck and enjoy it.?