Based on this product's specifications, here are some alternatives and similar models
Self-adhesive C4 Mailer envelope MAILmedia 383848 — 90 g/m², grey
Summary description:
C4 self-adhesive mailer from MAILmedia, model 383848, made of 90 g/m² grey paper. Designed for sending A4 documents without folding, it features a peel-and-seal closure for quick sealing and a durable paper construction to protect contents during transit. Suitable for offices, print shops and businesses that need reliable document mailing with a professional appearance.