I want to calculate the price at $t$ for such payoff at $T$ $$\max(S_T,S_{T_0},C),$$ $$\max\left(S_T,\min(S_{T_0}, C)\right),$$ $$S_T -\min(S_{T_0}, C),$$ $$t<T_0<T.$$ Is there any way or reference to simplify above payoffs. Since it seems much complicate than a forward start option.
How to obtain the closed forms under BS model (If some of the payoffs have the closed forms)?
Actually I use the stochastic vol model and have to numerically solve the price. I want to investigate the relation between some risk sensitivity and the parameters controlling the forward skew. So is there any way to simplify the payoff or approximate to some vanilla payoffs?