My three have floor time at least 5 times a week.
Like you we put down a fleece blanket with an outdoor metal run on it.
They do still need some shelters and hideys though, so the spaces isn't overwhelming.
We try to arrange things differently each time, and add in a few of the following; old cardboard boxes and bags, a tunnel or two, a hay box, a pigloo, a pile of fleeces or towels to burrow in etc. The kids set the run up so they get to choose how it looks each time, but they always leave a 'race track' around the edge of the run so the piggies can get up some speed when they are feeling athletic!