I don’t follow Montessori per se but I understand the sentiment. I like open ended toys so we have things like magnet tiles, lego, wooden trains and train tracks, and so on. Basically toys that can be played with in lots of different ways and that interact well with each other. The magnet tiles can be train stations but he can also build a house with them and has a basket of wooden doll house furniture and little people to put inside.
As for making the house more “Montessori” i.e. set up in a way that young children can be independent and participate in daily home life, you can’t beat Ikea. You can get everything you need at Ikea. Our favourites are the flisat table, “real” cutlery and crockery/glassware in kid sizes, coat and bag hooks, shoe storage, small milk jug, wicker baskets, mirrors low on the wall, low down in the bathroom, step stools etc, all perfect for kids to help them have autonomy at home.
Most things labelled “Montessori” are either cheap crap, or the total opposite and the prices are marked up just because of the Montessori label. I also think so many are such a waste of time. Kids don’t need specialised toys. Before they’re old enough for things like magnet tiles, lego and train tracks, mine was happy just playing with odds and ends around the house. You can replicate any of the so called “skills” by yourself. An empty box of tissues can be filled with cloth handkerchiefs to pull out, make ramps with cardboard to roll things down, tape kitchen roll tubes to the wall to make marble runs, create your own treasure basket and fill it with wooden spoons, a metal whisk, bits of different textured fabrics, crinkly foil blanket, containers with lids and things to fill them with, a small handheld mirror, a soft brush... This way you won’t end up with a house full of “toys” that are outgrown in the blink of an eye. Save buying toys for when they’re old enough to actually enjoy things like doll houses, duplo, trains and so on.