For lomo-style digital photos, the camera type matters much less than the lens, handling, and post-processing. A DSLR and a mirrorless camera can both give you the sharpness, resolution, and color contrast needed for large prints.

Mirrorless does not inherently give “better color” or composition. Its main practical advantage here is size and weight, and the shorter flange distance makes it easier to adapt many old film lenses, which can help if you want vintage character, distortion, softness, or unusual rendering.

DSLR advantages are typically larger sensor options, an optical viewfinder, and a more mature lens/accessory system. But for a lomo-like look, those advantages are not decisive.

The look you want mostly comes from style choices: saturated color, distortion, shallow depth of field, softness/glow, and out-of-focus effects. Much of that can be created with lens choice and editing rather than the body itself.

So choose the system you’ll enjoy carrying and using. If you want flexibility with adapted vintage lenses and a lighter kit, mirrorless may suit you well. If you prefer the DSLR ergonomics or available lenses, that will work just as well.