Maybe you can help me with a problem I have in using OLS regression:

I have a dataset of 12 markets, in total ~2.5k trades happened over all markets.

I now calculated 6 different measures for the each markets performance (my 12 observations per measure i want to use as dependent variables)

My treatment is indicated by a dummy, 6 markets were in one treatment, 6 in the other one.

What I would like to do is, to use OLS to see, if there is a treatment effect, using the dummy variable, looking like this:

Y = cons + b*dummy + e

My question now is: Can i do this without overfitting? I dont know if I can use OLS because of my low number of observations, even though they stem from far more (and hopefully carry the statistical power / information of all my observations of transactions?)

I would also like to add (2-3) control variables and am worried that I will use too many explanatory variables on too few observations.

Thank you very much vor any help!