Saxmundham Carlton Park. Its a sports ground that has a campsite behind it. Good, clean toilets and showers (even a large family one). There are 2 washing machines, a great spinner for draining clothes that you have hand washed, a freezer for ice bricks and a couple of sinks. Its well kept. Its spacious and has a fab play area for children just off the site.
If you do go, try and camp at the top end of the camping field as there is a factory behind the bushes near the tennis courts and you can hear the fork lift all night.
The Orchard in Wickham Market is supposed to be good and you can have a cmap fire. Its booked up for all weekends during the summer months though.
I have also been recommended Rendelsham Forest near Woodbridge by 3 different people.