If you add slime to your tubes please do not bring it to your local bike shop or if you do warn them in advance and maybe bring them a beer or two to drink after they get slime everywhere. That stuff is nasty and unneeded. If you are having frequent flats and issues, make sure you have a good puncture protectant tire that is properly inflated and try to avoid jumping curbs, running through glass and other road detritus and check your tires once and while for any signs of wear or puncturables. If you are worried about small punctures switch to tubeless tires and then you can use proper sealant (which will still make a mess eventually but is slightly less terrible than the regular slime (though slime does make a tubeless sealant which I may try at some point since I have a bottle given to me to try)

If you are really desperate you could try a small amount of sealant in your tubes but it is just extra mess.