Buying defenders and full-backs is not the rescue in my opinion. We are in desperate need of two playmakers with pace, technique, creativity, flair and vision and one attacker full of pace. With a stronger attacking unit the defence will be stronger as a result.
In A 4-3-3 that would be Pickford - Baines, Jagielka, Holgate, Coleman - Gueye,
?(in desperate need), Schneiderlein - Richarlison,
? (In desperate need), Walcott. Bolasie, Lookman, Mirallas could all make an impact as substitutes due to pace and skills. It would be nice to have back-ups/alternativer for our full-backs and one more skillfull pacy DC too but first Fix the striker and midfield positions as Tosun, Gylfi, Niasse or orher options will never create chances for us...