Alexa Fluors will indeed work, but depending on your fixing and processing protocol, you might find them substantially quenched.
In the past I have used low molecular weight dextran conjugates, that are tagged with a fluorophore and a biotin moiety. These labels diffuse fairly quickly, are fixable, fluoresce on their own and the fluorescence can later be enhanced by using streptavidin tags during the tissue processing. I used this to reconstruct cerebellar parallel fibers, and the labeling was great.
Invitrogen/Thermo offer compounds like this, e.g. MicroRuby:
If you want to go more classic, try luciferyellow. It fills cells nicely, is fixable and stays bright after fixing. You will need fairly high concentrations, though, so the lithium salt (rather than potassium) would make sense. Do keep in mind that lithium interferes with slow calcium signalling by modulating enzymes in the IP3 pathway, so if that is what you are interested in, LY is a no-go.
I would highly recommend 3-4% of neurobiotin in the patch pipette. After fixation and processing with streptavidin you will be able to see clearly not only the somas but also processes.
One thing to keep in mind with Neurobiotin and Alexa dyes is that they will cross gap junctions. Depending on your cell of interest that might be an issue. But it doesn't have to be.
Regarding the bleaching of Alexa Fluors during fixation, at least for some of the common Alexas, antibodies are available that can be used to boost the signal, if you find that you do not get sufficient labeling intensity.
I have only ever used Lucifer Yellow, but that is because I am "old school". However, here is a link to another researcher here on RG that had good luck with neurobiotin:
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