Hi sindrenogva,
Welcome to the TechForum.
In general, the larger the size of the antenna, the greater the range. How you intend to mount it and the materials used around it will also affect performance. Here’s a link to antenna designed for HF frequencies and which meet your physical dimension limits. You’ll want to peruse their respective datasheets for options such as having rear-side adhesive or ferrite material for shielding/signal enhancement purposes. (See this note for more on that topic).