Floaty scarves, foil blankets (both already mentioned by PP, I, just agreeing). Toys that make different noises e.g. a rattle, a bottle full of pasta, a bottle full of rice (google “making sensory bottles”) for ideas. Different pieces of fabric for different textures - or you can just read “that’s not my” books for this aspect. Disco balls etc for lights - there’s lots of different types on Amazon, mine love the cheapest ones and they are battery powered, so very portable for play. Look around your kitchen for different textures e.g. one wooden spoon and one metal spoon of a similar size. Different smells - get different tea bags (mint, chamomile) to wave under babies nose and get a couple of fresh herbs e,g. Basil, rosemary, lavender. Or if you prefer, get a humidifier and different scented oils.
Bubbles bubbles bubbles. Use the same music over and over again for play so that they start to associate it with playtime, then they get so excited!
Tummy time can be very good sensory time. Get different things for them to lie on - I’ve got a woolly mat, a fluffy blanket, some smooth scarves, foil blanket... I’ve also got some of those ones you can put water in. Sometimes I make it warm, sometimes I make it colder (but this limits how long baby can be on it). You can also sort of roll them over a big ball for tummy time to help them develop Balance,
Classes are now open though. We went to our first one this week (did it a few years ago with eldest). It’s not as good as pre-COVID, but I thought it’d be good for my little ones to see other babies and I’m sure it was.