There are a lot of potential options. Some of them are even actually planned to be able to start families with vag!Champ.
Of the 24 non-generic ladies with penises in the game, 6 can currently get Champ pregnant (Arona, Fritte, Hashat, Oxana, Meira, Orlaith), 1 can kind of get Champ pregnant (Kasyrra, depending on how you feel about imps), 4 are definitely off limits (Aurera, Naiyana, Nareva, Synneva), and 13 might be available to have kids in the future, ranging from "almost certainly not" to "virtually guaranteed" (Anna, Edessari, Etheryn, Eryka, Evelyn, Jael'yn, Lyla, Mara, Morwen, Syrish, Valencia, Wredi, Yani).
Of the 50 non-generic gentlemen with penises in the game, 8 can currently get Champ pregnant (Berwyn, Brint, Quin, Elaril, Garret, Imad, Lyric, Nyze), 11 are definitely off limits (Barney, Garth, Jarl Gunvaldsen, Keros, Mallach, Nash, Ogrish, Philander, River, Sanders, Svern), 3 are cultists (so almost certainly not), 1 is Argoth (so I have no idea, but you'd have to ask Savin), and 27 might be available to have kids in the future, ranging from "almost certainly not" to "virtually guaranteed" (Behemoth, Boomer, Dale, Darius, Elyon, Fenraus, Hinata, Hirrud, Hitoshi, MMM Jerk Merc, Jin-Jin, June, Kazuo, Leofric, Liulfr, Livernus, Nakano, Ninian, Pavo, Raphael, Rooh, Rrojlar, Sugo, Taldahs, Takahiro, Vaush, Vicky).
None of this counts eggnancies like those by Azyrran or the Drider Queen, or alraune seeds. Nor does it count characters that are written and unimplemented, or unwritten but planned.