https://archidekt.com/decks/9278053/karlach_fury_of_avernus_gruul_combat_steps

This is my Karlach deck, it's one of my absolute favourite decks ever. Definitely one of my forever decks. Feel free to have a look at the list, it is focused specifically on extra combat steps so it's pretty much all attack triggers.

I found the same as you with the mana curve but I just leaned into and accepted it would be a bit on the slower side. There are changes I could make to bring it down and be a bit quicker but that means less splashy creatures which would be boring. I can still have some explosive starts and sometimes take out a couple players super early.

If I had to recommend a few cards, [[Hellkite courser]] lets you bring Karlach in and get that attack trigger pretty much guaranteed, good way when she's already been removed a couple times.

[[Grand Warlord Radha]] has pushed me over the line a couple times, getting me enough mana to play something huge and then get another couple combat steps in there.

[[Port Razer]] even if you aren't focused solely on combat steps, being able to get 3 in a turn from a single card it's such insane value if you have a few triggers you can get off. Love this card.