I dont think that you can convert gold into trophies. The easy way is always real money, but if you want a slower free method there are a few.
The easy way would be "arena challenges" the first 20 are relativ easy and you get ~56 trophies for a win, if you do that with your first 4 glads you can save quit a bit for later "real" glads.
Every tavern quest has also a low chance for 1-5 trophies (you likely wont farm that much from it, but sometimes the extra 5 trophies are all you need)
The more advanced way: there are top 10 fights in each bracket daily, the winner gets some trophies ~30 I think. You can place 1 or more glads in one bracket in the top 10 and farm some trophies, if you stay for some weeks in the same bracket (it is easier than one might think, most good glads advance fast leaving only the fodder glads in the bracket)

Trophies are only a time saver, you dont need any trophies for the late game. "time saver" even with trophies you have to spend some months to reach the late game.

PS: you could make a "slave" glad and farm the first 15 arena challenges and sell him to buy a new glad for the same purpose. That is only recommended for non HoL glads and will waste a howl slot in your stable.