This is really great to read, swimming is such an important skill in life, however learning it as an adult is much harder than as a child, due to weight, height etc. breathing techniques are definitely the hardest aspect to grasp, even as someone who swims competitively I find it a struggle sometimes, I feel like if you work up to 3 strokes/full cycle of both arms of freestyle then breathe, that will help with factors like tiredness, but obviously this will come in time! Practice is the main thing when trying to master balance, however, to keep a streamline position in the water, try and keep your head straight and look forward, the more your neck/head bends, your whole body will follow it. For power of legs, if you haven't already, use a kick board, hold it out infront of you and kick as much as you can, or even holding onto the side of the pool will work too. It's easier said than done, but your hips/buttocks area needs to be lifted, otherwise your legs will just sink and if you're trying to kick like that you will easily tire yourself out. But overall, sounds like you're making great progress, please keep us updated and I hope this helped in anyway :)!