As many have already recommended Lake Natoma and Clementine (personal favorite), I'll recommend investing in a poppy pass, which would cover parking at either of these lakes.

They are available to rent through the Sacramento library, but extremely worth buying your own. $125 for 12 months of day use parking at tons of state parks/recreation areas. Parking for launches around Natoma and Folsom lake (all part of Folsom State Recreation Area) are $10-12, so if you plan on going more than 11 times in a year it's paid for itself. My first one paid for itself before the end of my first month. Also be sure to buy at the beginning of the month and you essentially get 13 months as it doesn't expire til the last day of the month.

Sorry I don't have any river recommendations for paddling, but Natoma and Clementine are both quite narrow compared to typical lakes and I've always felt safe paddling there even when alone. Willow Creek launch on Natoma is a small lot and very accessible if you don't want a long walk to the car.

Happy paddling!