And also keep in mind that if you use dual lands, even if they give you 2 life they will enter tapped. If you add 3-4
evolving wilds to your deck and then trimmed the dual lands down to maybe 1 of each (depending on what the deck's main color identity will be) and keeping all your tri-color lands then your mana base should be fine. You're running a 60 card deck so your mana should really be between 22 (on the low side) and 26 (on the high side depending on the deck). Usually I would just sit at 24 as the default because it's a safe number to play without getting mana flooded constantly.
Also I would recommend switching out
through the breach for a lower costed card but with something of equal value. For example, if you include
call to the kindred then every turn you can drop a new creature pretty much straight from your deck onto the battlefield without having to worry about casting costs. As long as your enchanted creature stays
alive you are basically receiving a free creature every turn. Also adding
diregraf captain will give all your zombies a power boost and it'll burn your opponent every time they die. Since your
grimoire of the dead turns the creatures it brings back into zombies, anything that dies after that point is basically free burn damage. Creatures such as
black cat would become an investment,
butcher ghoul is a fairly low cost card that naturally has undying, and
sanitarium skeleton will help with any discard costs for other spells.
Here's another idea for you, if your deck focuses around dropping creatures in the grave for recursion then why not assist that way as well? If you use
altar's reap then you can sac a creature that has undying, get free cards and the creature comes back stronger.
bone splinters would be great to have at instant speed,also if you want to get tricky you can use
corpse traders. Basically sac a creature (works in your favor) and discard ANY card that your opponent has that you don't like. It can only be used on your turn but its effect includes LANDS. So say goodbye to your opponent's mana base.