I always ride with a breastcollar, always have. Yes granted they "help" keep your saddle in place, but honestly you don't need them. If your saddle is slipping you need to check the fit of your saddle, and also your pad.
When I don't ride with a breastcollar my saddle doesn't slip. I always trail ride in one though.
I always put one on just because my horse looks good in the one I have um I would recommend a three-point hook for you because you said you just started western I ride in a tripper breast collar which is really just for roping and cutting though I use it for barrels and team penning. Three points are just alot easier to fit to a horse even though a tripper would look easy they do get their name for 1 reason they tend to trip your horse alittle if they arent used to it. Can be a major problem but most of the time alittle trip isnt that bad but trippers arent for beginners.
This is a three-point hook
these are some of my trippers that I have in my tack room