The only place to stay in the Pantanal itself, this is an attractive wooden lodge with ceiling fans overlooking the Río Negro, an hour or so west of Bahía Negra by boat. You should reserve your visit in advance with Guyra Paraguay in Asunción to organize a boat transfer. Electricity is by generator only (25,000G per hour).
Ask Tres Gigantes about providing food; if it isn't possible you will have to bring your own, but there is at least a kitchen you can use.