Hi - Best place is just over the border in Essex at Camperite. They are based just off the A12 at Marks Tey. They have lots of tents on display outside and a well stocked shop. I've bought a couple of tents from there as well as several accessories. Dave is his name and knows everything you need to know about tents!
Depending which end of Suffolk you are, you could also try Cross Camping and Leisure at Melbourne, Cambs. My Mum lives in Suffolk and we often go there on the way to her. They've got a big outdoor display as well as a good indoor equipment store.
Maybe to late - but either camperite at Marks Tey or ask at your local millets as some have tents on display, if not they have tent shows (we bought our tent last year from Ipswich tent show)
Another bit of a drive but Norwich camping and Leisure at Blofield Garden Centre just off the A47 (Go A12 to Yarmouth then A47 towards Norwich) have a huge display, loads of kit indoors, a nice cafe to sit and ponder your choice over coffee, and loads of friendly helpful staff. Yo can check them out on the internet first but I'm not smart enough to put a link on!!
Hi we live in suffolk and went to norwich camping and were very impressed. we went home and decided what tent we wanted and ordered it by phone (got them to price match) on the sunday and the tent was delivered on the weds. when we pitched it at home we found we had some pegs missing ,phoned them up and we received a whole new bag of pegs by courier the next day. we have been very impressed with their service
Another thought. I haven't been to either of these places but have spoken to them on the phone. Stowmarket caravans have some tents pitched behind their caravan sales area and Geoff Turner, also in Stowmarket have tents pitched in their upstairs showroom.