Suggestions for financing first couple of properties

I have a financial partner with whom I have done all of my rehab and flip projects and we are able to pay cash for everything, no bank involved. 

I am looking to start building a portfolio of rental properties however my partner is not interested in buy and hold, simply continuing to do rehabs. 

Any suggestions on how to go about financing these projects? Do I go the conventional route and get a 20 or 30 year mortgage to start on the first couple? I have a sizable amount of money saved up and ready to put down 20%+ on my first 2 or 3 buildings but am not sure if that is the best way to tie up my money at the beginning.   

I could have another partner with some cash to team up with but I am not looking to necessarily add another partner to the mix. 

Any suggestions for getting started would be appreciated.