I usually stay at The Royal Yacht in St Helier, and can highly recommend that - though I have found a large variety in the size of a double-room, and you would want to ensure that they gave you a decent option.

I've also stayed at the Grand once too; that was perhaps slightly nicer than the Yacht, though more expensive, but you might be able to get a sea view overlooking St Aubin's Bay.

Other places I have been recommended but never visited are L'Horizon and the Atlantic Hotel. The Atlantic, in particular, is on the pricier end of the scale and both are out of St Helier so you would need to organise transport, but equally Jersey as an island is definitely worth exploring. You can hire a car for not-very-much per day.