Subbing flaked oats for base malt

I have a (2.5 gal) stout recipe that looks like:

5 lbs 8 oz base malt
5 oz black patent
3 oz roasted barley
2 oz carafa iii
2 oz caramel 120

My question is - if I substitute the 8 oz base malt for 8 oz of flaked oats for some added body - will it affect the fermentability and final gravity of my wort?

I like this recipe as it is, but I think it would be even better with a little extra thickness.

That would work fine. The remaining base malts would convert the flaked oats.

Excellent, so no harm in ending up with only 80% base malt?

I am fairly toasted off of the normal version of this recipe... yay stout!

Look up how to calculate the Lintner of your batch. I'm on my phone or I would give you a good link and some more detail.

I did a little skimming on Lintner calculations and it looks like even in a totally worst case scenario, if none of the other malts besides my 2-row had diastatic power, I'd be fine?

One site I checked had 140 for the Lintner for US 2-row:

[5 * 140] + [0.5 * 0] + [0.1875 * 0] + [0.125 * 0] + [0.125 * 0] / 6.25 = 112