Hi. I'm playing in a campaign as a tiefling warlock with the hexblade pact. I just reached level 5 and got my extra attack. The problem is that I feel like I'm wasting my first round casting a buff spell like mirror image, so I was thinking about multiclassing into sorcerer (shadow) so I can quicken my spells and still attack.

if I read the multiclass rules right it says that my warlock casting does not stack with any other type of casting. Will it make my character bad if I take sorcerer and then I'm behind by 5 levels of spells? How should I build this?