If you have enough money to invest then you can invest. If you don't like the market at the moment then you can continue using the DCA method because investing in the DCA method will give you a better investment method and you will have a higher chance of success. But you can use electum wallet or trust wallet to hold the investment but the wallet seed must be kept very safe.
I have been using trustwallet for quite some time but to be honest, it is not the most recommended wallet for newbies and even for those who are no longer a newbie. Electrum should be the best choice between the two that you have recommended to OP which is much more safe than trustwallet and it is not close source. Ways of acquiring BTC like DCA would be a good decision to make if you don't have lots of money but wanted to buy more once you have money.