I don’t really know of any grammar resource that will ask you to know a bunch of kanji before you can make it through.
That’s not to say you shouldn’t feel the way you do about waiting, I just don’t understand the sentiment expressed by Koichi.
For instance, in the 3 volumes of the A Dictionary of Japanese Grammar series, everything has furigana until the Advanced volume. And even in that volume, there is furigana on more difficult kanji.
BunPro is very similar to wanikani but focused on grammar. It links to many other sources from book pages to websites, to videos, so you can learn from them and organize your studies on BunPro. It’s still free for a couple of days and it will still be pretty cheap after.