I am thinking of putting sealant in the inner tube that way I don't have to buy expensive tubeless tyres and it will still be easy to change the tube if I need to. I don't know if it will work as I have not tried it yet.
You can buy tubes pre-filled with sealant - "Slime" branded, usually.
Generally, sealant in inner tubes doesn't work as well as sealant in tyres.
You are best off if your tubes are a little oversized, so they aren't stretched much, if at all, when you pump them up. Something like a 32-38 tube in a 28 tyre.
There's also the matter of finding tubes with removable valve cores, so you can add the sealant without clogging the valve.