Flex and WR starts

Need some help on who to start this week in my wr spots and flex.

MT - could see huge volume cuz you know KC is gunna score. He also already has a high floor.

Lockett - high ceiling but is a gamble every week

Kupp - smash play but could just turn into the Cook show limiting Rams use for WRs in this one

Jefferson - tough matchup but I trust the rookie so probably starting him

Well I guess MT is out of the equation now haha

However, now that Mostert is in play would anyone slot him in the flexspot?