It's expensive, but Jeweled Lotus is amazing in Muldrotha. You can fetch it with Urza's Saga and recur it.

Speaking of Sagas, they're amazing in muldrotha, I run The Cruelty of Gix, Binding the Old Gods, The Phasing of Zhalfir, Phyrexian Scriptures, and I am testing out The War in Heaven. Those probably would work better than Oblivion Stone.

38 lands is a bit high, you can probably get away with 34-35, even 33 if you're willing to invest in Mana Crypt and Mana Vault.

In my hands, Muldrotha has been running better as a combo cEDH list. I have tried to build it other ways and it was honestly either too slow or too samey to my Zegana and Miirym lists. I think combo would work better, Muldrotha loves self mill and that can act as a sort of turbo way to draw through your deck.

If you're wanting to stick to ramp, you're going to need to speed it up

A good ramp package I use in U/G and U/G/X lists, tweaked for Muldrotha:

1 drop: 1-3

Sol Ring

sometimes Birds of Paradise and other related mana guys

for Muldrotha: Expedition Map and Wayfarer's Bauble will do wonders

2 drop: ~6

Arcane Signet

Bloom Tender: I play this in almost every 3+ color list

Farseek

Three Visits

Nature's Lore

Muldrotha Specific: Sakura-Tribe Elder, Skull Prophet, Rootcoil Creeper

3 drop: 1-2

Uro, Titan of Nature's Wrath: hilarious to recur every turn

Cultivate, Harrow, Springbloom Druid are all good too

You will also want some more heavier hitters up top, generally, in ramp heavy decks I will run anywhere from 8 to 15 (depending on how well I ramp). I want to be able to have a big finisher and keep them going in Ramp lists (you can see these 2 to see what I mean: Nature's Revenge (not recognized by brackets for some reason) and Baby Dwagon Ehhhhhh?, both are very powerful and keep the pressure up, I rarely have an issue with either too many big guys and not enough ramp.

Sire of Stagnation

Toxrill, the Corrosive

Koma, Cosmos Serpent

I've been loving the ancient dragons

The other Jin-Gitaxias is also pretty potent

Here is my list if it helps give any ideas to help yours: The Circle of Life

Note:

Massacre Girl= Primaris Eliminator

Noxious Gearhulk= Necron Deathmark

The Eldest Reborn = The War in Heaven

I don't think I have put the combos down in the description yet but I can explain them if you want to know. Hope this helps!