My first successful sourdough sandwich loaf

I've been trying for a little over a week now to make a sourdough sandwich bread for my family with only a starter sponge, flour, water, salt and olive oil.  FINALLY after many flat attempts, I'm successful!  Obviously this is not a very stunning loaf but I am very proud, never-the-less.  It tastes very good and I love that I just used a little baker's math to do it!   It didn't have much oven spring, could that be from over proofing?  If so, that is an absolute first for me!  I didn't use steam because I thought it was making my other sandwich crusts a little on the tough side.  Also, I chose to put them in the oven when it was around 250 first thing this morning because I was concerned about the overproofing.

Now, to find something more fun to focus in on! :) 

ETA:  While this still tastes very good, I've noticed that I prefer the texture and crumb of my recent slightly underproofed breads (with blowouts).  This loaf is a wee on the spongey side, almost reminding me of the No-Knead bread.  Overproofed?  Any feedback is welcome, I'm very new to sourdough! (the sandwich is the underproofed)

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