Did you replace the Bel Cantos? If your strings are not old then you likely need to get a soundpost check to see if you can help that E string. You should be getting enough sustain on that E string with a Spiro Weich. I'd do that before buying more strings.
I have confirmed the strings are not belcantos, but Spiro Weich's. Sound post was checked before purchase and seemingly good, although the luthier did notice some damage to the top around the sound post.