If you really want a 3rd level stance, then you need to multiclass two levels before you reach warblade 4. Otherwise, you are stuck with two 1st level stances until level 10 unless you spend a feat. That's not necessarily a bad thing, but this may bother some people, like me. They screwed up the stance progression for all three classes. Alternatively, ask for a house rule to allow the changing of a stance known at 5th level and every 5 levels thereafter.

A good option is to multiclass fighter for the two levels. You get proficiency in heavy armor and bows. BAB continues to increase linearly. You get a nice bump in fortitude and Moment of Perfect Mind handles the will hit. The big deal is two bonus feats to play around with. You can still take Weapon Specialization if you want it at level 6 as a Fighter 2/Warblade 4 just as you would as Warblade 6.

The cost is 2 average less hit points, a slight delayed gratification on gaining maneuvers but you still get 9th level maneuvers before level 20, and no Stance Mastery before Epic. Still, most campaigns end before level 20 anyway, and even if you do play to level 20 and beyond, the time spent less than 20th level is a lot longer than 20th level and above so you get a lot of mileage.

Alternatively, multiclass Crusader or Swordsage. Crusader gives you the armor, bows, Devoted Spirit if you want, and extra Stone Dragon/White Raven slots to help qualify for higher level maneuvers without using up Warblade slots. Plus, it becomes worth it to spend a feat for Thicket of Blades if you really want it. Swordsage gives you a lot of maneuvers, helping a lot in Stone Dragon, Diamond Mind, and Tiger Claw slots for higher level prerequisites. If you don't need to make a will save that often you can pick up Moment of Perfect Mind here to have more direct actions available in your Warblade slots. If you're going to take Adaptive Style feat anyway, Swordsage couldn't hurt.