Hi! I'm homeschooling my precocious preschooler (almost 3). I do my version of Montessori. She picks the activities to complete everyday, I have an idea in my head of what we will cover that week or during the month but it's her choice as to what we will do each day and how long we will work. The easiest "curriculum" at this early age is the all in one workbooks you find at Sam's Club/Costco. I will move into a more formal curriculum as she is more school aged. These give me a format to follow for days she wants to do "book work" but we also have letter magnets to practice letter recognition, we play I spy for colors and shape recall, we count every thing to practice numbers... She is involved in daily activities of our house, she helps me cook meals (pouring and mixing mostly), cleaning up her plate after a meal, and keeping her toys picked up.
Much of the Montessori concept is child led, allowing the child to explore concepts at their own pace/way (I have seen Kindergarteners who have the concept of multiplication and division down). I used to teach at a Montessori school (elementary and middle school aged kids, so I have no experience with preschoolers!) and realized something must work because I had middle schoolers arguing over who got to sweep the classroom at the end of the day! That's unheard of with that age
My advice is to hang around here, ask lots of questions, and not to worry! I don't see a need to spend much money on a preschool curriculum, especially if you are using the Montessori method. Early school is more about exploration of ideas and the world around them!