So I guess you've chosen L for 10% ripple in CCM (continuous conduction mode: inductor current does not return to zero each cycle)?
This is usually excessive. Modern core materials are happy with >30% ripple, so you can save cost and size on that.
To stabilize a CCM converter, you need average current mode control, which requires sensing the inductor current at all times. However, the current is constantly alternating between primary and secondary side, so this is complicated to do. A current sensor on L2 may do; I'm not entirely sure. I think it would help to have LM/L11 be a transformer (relatively high inductance) so that L2's current is the primary control variable.
A DCM converter has >100% ripple (i.e., current goes to zero each cycle), and can be operated with a peak current mode controller instead. Which is usually cheaper, because a shunt resistor on the switching transistor is sufficient information. Ripple is much higher, obviously, so lower-loss materials are needed, and more bypass/filtering, but this is quite practical for smaller converters, under 100W or so.
In any case, the transformer's coupling coefficient will need to be as large as possible (0.99999 is probably not possible, mind), and it will need to be damped on the primary side with an R+C or better snubber network. This will increase Vds(pk) further, affecting transistor choice.
Tim