I've layed out lots of SMPS & in general lack of space is an issue on them - It's quiet difficult to predict how long the layout will require to complete, & there are compromises to be met all along the way. The best piece of advice I can give is to be patient, expect a lot of ripping up & trying again, even with experience they can be difficult. Make sure your I/O pins are optimally positioned, keep gate drives short & switch nodes as isolated as possible. If necessary use blind &buried vias to isolate digital & analog ccts.