We have regularly used 'Le Vivier aux Carpes' as a convenient overnight stop, both on our way further South, and as a stop before catching the ferry home. It is an excellent little site, well kept and friendly, and manages to maintain a French ambiance, despite having many British visitors.
The village has a small shop, and a bread van calls at the site in the morning. St Quentin is within easy reach for other shopping etc, and the WW1 Battlefields and memorials can be easily visited. Fishing is available on the site.
If you just want a very relaxing holiday, Le Vivier will suit you fine. If you think it might be a bit too relaxing, why not have a few days there at the beginning and end of your holiday, with a few days somewhere else - I would suggest Burgundy - for perhaps a week in the middle. But really, it depends what you feel most comfortable with. Whatever you decide, I am sure you will have a great holiday.