We use a water based lube as it is safe to use on silicone toys and my (Zec) favourite is the Durex Very Cherry Lube from Lovehoney. (It is sold as Very Cherry or Cheeky Cherry)
Silicone based lubes are silicone soluble, which basically means it will react with silicone sex toys and literally melt them and so it is always best to use a water or oil based lube.
I like the Durex Very Cherry because it’s great for oral sex and the taste is very good.
You should of course always use a lube when you use sex toys and also it’s perfect for masturbation for him or her.
The 50ml Very Cherry (or Cheeky Cherry) comes in a plastic squeezy bottle and costs £4.99 from Lovehoney