We need a top GK to push Robles back on the bench (Timo Horn/Yann Sommer from the Bundesliga would be good purchases); LB to push Oviedo (Garbutt isn't good enough and Baines is finished for a team with our expectations); RB cover for Coleman; CB to challenge and ease Jagielka out the door (a partner for Mori, as Stones isn't a CB at all and will probably leave in the summer anyway); an out and out playmaker good enough to force Barkley back into a CM position (Dowell will be good enough in the future but not now); a pacy left winger with a box of tricks (Mertens type) to compete with Niasse (obviously sell Mirallas); another forward to deputise/partner for Lukaku (a Giroud type that can offer a physical and aerial threat if we have to go more direct in games looking for a breakthrough).
You're looking at a cost of circa £60M-£70M for that lot - most of it funded by the sale of Mirallas and Stones, who should fetch £10M and £40M, respectively.
Have you seen any of those two keepers play before? Baring the odd game here and there? And what makes you so sure that Mertens is better than Mirallas? Similar players to me. You're writing a lot of players off here too early IMO. Jagielka can play on for another 3 years at least, Baines is still getting over a bad injury, there are no certainties that Stones will leave nor do I believe Niasse was signed to play on the wing.