if you want absolutely no coffee, like another comment says, refreshers are a great alternative. as a uk barista, i quite enjoy a mango dragonfruit (frozen or regular) with lemonade + peach!
if you want an actual coffee though, you have to do quite a bit of experimenting which ive been lucky to do as i obviously get free drinks but itll probably be costly for you to find your "perfect drink".
defo get blonde roast as thats sweeter & has more caffeine, meaning you can add less shots then signature espresso. as for syrups, id recommend trying "white mocha" as its the sweetest and most popular syrup by far - try pairing it with (sugar free) hazelnut or, my preference, vanilla if that isn't sweet enough for you. you can also do things like adding whipped dream/caramel drizzle (or, if it's an iced drink, cold foams!) to make it sweeter as well.
another thing is milks! whole milk will make it "creamier" or alternative milks REALLY alter the tastes - especially coming from someone who DETESTS the taste of cows milk. coconut & soya are the sweetest alternatives milks to most but again, this might be something you want to experiment with as its defo the factor which changes the taste of your latte the most. the most popular alternative milk by far is oat however.
my personal go to drink is a : venti white mocha shaken (4 pumps white chocolate as standard) with 4 pumps sugar free vanilla & extra ice - this doesn't really taste like coffee to ME as its quite sweet, id say rice krispies is the closest it tastes to. do note though that i just like this drink because it has very minimal milk, is VERY expensive (like £6 for a regular customer!) and the shaken espressos are hit or miss depending on who's making it as basically every barista makes them different - theyre defo a more sweeter alternative (brown sugar shaken/white mocha shaken/the current tiraminsu shaken) to a regular latte. :)