Why do you want to move away from your current solution which involes a relational database? I wouldn't (believe it or not) recommend to change your datastore premature.
If your are experience problems and want to replace your relational database, then I would recommend to investigate Apache Cassandra.
If you find Cassandra interesting I would suggest a data model that looks something like this:
Commands = { // this is a ColumnFamily (CF)
commandObject1: { // this is the key to this Row inside the CF
// now we have an infinite # of columns in this row
field1: "value1",
field2: "value2",
field3: "value3"
}, // end row
commandObject2: { // this is the key to another row in the CF
// now we have another infinite # of columns in this row
field1: "value1",
field2: "value2",
field3: "value3"
field4: "value4",
field5: "value5"
},
}
(thanks Arin (and his excellent blog post) for the Cassandra data model notation)