Spicing it up

Hi guys! I've been trying to spice up my sex life a little bit with my fiance. I feel like sometimes he finishes too quickly, and then I'm left hanging, wanting more .. he won't continue if he's already finished. I've tried to ask him numerous times about possibly getting some sex toys or something to add a little variety. He thinks that I do not enjoy our sex just because I want to add sex toys in bed ,which is obviously not the case. I've tried explaining to him it's just because I feel like sometimes I could go longer, and different toys provide different feelings of pleasure and I want to experience that ,but for some reason he is not taking it the way I am intending.. I am also trying to convince him to go with me to pick some out so that I know that there's some he also would like to use on himself or on me but I don't understand why he just won't agree to go with me. I feel like if I go alone I'm not going to know exactly what to get or what he would like and then when I get home he will be upset that I did that. All I know is we need to spice things up or it's going to stay casual forever.. I'm not trying to be mean by saying that because although it's casual it still feels good... but it can be boring after years of the same thing. What do I do?