I recently bought the Toto Clayton without a seat and selected the seat separately. I believe most staandard elongated seats will work --

I'm certain a standard elongated seat will work. Do you mind me asking why you chose to not go with the soft close? We just installed an Ultramax w/ soft close in my husband's bathroom. Knowing you're not supposed to sit (with lid closed) on the Washlet soft close lid, I called Toto to ask about the other soft close lids. Not recommended to sit on those either. DH isn't terribly happy about that :(
Monica

We don't want the SoftClose because (1) we are able to close normal lids without slamming them and don't think the SoftClose feature is worth the cost, and (2) I just know that if I ever got used to the SoftClose, I would end up slamming toilet lids at other people's houses. And (3) I'll have to add not being able to sit on the lid!