concerned about milk supply returning to work .

Bi
I return to work when my son is 7 weeks (currently he is 4) and it's part time 3 days a week , I'm breastfeeding only no formula as I just don't want to use formula just yet but how do I get around pumping enough to keep him going while I am at work? 
My son has been cluster feeding for 2 weeks now 😳
Any suggestions would be great 
I have a manual pump but thinking of getting an electric one. Which would be better do you think? 
Thanks 

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