1) If this will be the only suit you own for suit-appropriate occasions, you might want to try to figure out which of the following you look best in -- dark charcoal suit, dark navy suit, dark brown suit, darkish tweed suit -- and buy that.
2) If realistically possible, get a tie in a conservative pattern with colors as per the following:
2.1) one color that "matches" the suit (this color within the tie can be darker or lighter than the suit, but should not "clash" with the suit -- e.g. if the suit is navy, then the tie's blue should not have any visible purple-ishness nor greenishness that is not present in the suit)
2.2) one or more other colors that you look good wearing (do not make your face look washed out, etc.), and also look good with the suit; preferably including some shade of blue or green if the suit is solid charcoal or solid dark brown
2.3) inclusion of bright color(s) in the tie is ok, as long as the tie's dominant colors are subdued
3) If the suit is solid charcoal or solid dark brown and the tie meets both criteria 2.1 and 2.2 above: I think the ideal shirt would be white or off-white with stripes or small boxes that are one single conservative color that matches one of the colors in the tie.
Probably best if the stripes or boxes on the shirt match the blue or green that is in the tie; second best if the stripes or boxes on the shirt match the suit color (gray or brown); probably too flashy-looking if the stripes or boxes on the shirt are red, orange, or yellow.
But if the suit is navy or tweed or not solid; or if the tie does not meet both criteria 2.1 and 2.2 above; or if an appropriate matching stripe-pattern or box-pattern shirt cannot be found: then the best shirt is probably solid white or solid off-white, depending on what makes you look better but also depending on what can be found.
Sorry if all that sounds gay, but if you are going to drop a bunch of money on a suit you might as well try to look good.
Sorry about your loss.