Calculate average mean FFT Magnitude in bins
Here the answer for those facing similar problems:

if your Fs = 44100 Hz (in my case) and you want fft resolution of 10 Hz then use fft resolution N = 44100/10 = 4410. 

You can then take just 4410 samples of signal or split the stream into segments (+ overlap) each = 4410 samples and directly average the bins (fft output).

FFT covers frequencies from -Fs/2 to +Fs/2 so you don't need to worry about single sided spectrum.

You better average the amplitude values from each bin directly(not the dB), then you can convert the mean to power in dB:

fft_mean = mean(ffts1,ffts2,ffts3,...);

plot(20*log10(f,abs(fft_mean))); %in dB