Hi izzy,
The first place to start with any mattress research is always post #1 here no matter what your weight or sleeping style (the basic principles are the same). It has all the basic information, steps, and guidelines you will need to make the most suitable choices (and connect with people that make or sell good quality and value mattresses and can provide you with the best possible guidance in terms of materials that would be suitable for your higher weight).
As you can see in mattress firmness/comfort levels in post #2 here … I can only speak to the quality or value of a mattress or help with “how” to choose because there are too many unknowns and variables for anyone to make specific choices for others based only on very limited information.
With your higher weight though the materials and components in a mattress will soften and break down much faster than the norm for other people so it would be particularly important to choose the highest quality and most durable versions of any material you prefer to use in a mattress (whether they are innersprings, memory foam, polyfoam, latex etc). Firmer choices will also be more durable (and feel softer to you than they would for people that are lower in weight because you will sink into them more). You can read more about some of the factors involved in durability in post #4 here.
No matter what your weight or body type … the combination of PPP (Posture and alignment, Pressure relief, and Personal preferences) that is most suitable for you is just as important as it would be for anyone else. You will just need firmer and more durable materials and components in the support and comfort layers of a mattress to achieve it than someone else who is lighter. Who you choose to deal with and their knowledge, experience, and integrity can also be one of the most important parts of making the most suitable mattress choice.
If you let me know your city or zip I’d be happy to link you to the better options I’m aware of in your area.
Phoenix