For travelling with a 2-year-old, is there an inflatable toddler travel mattress/system that is recommended and/or recommendations of what to avoid when purchasing a travel mattress? We will be travelling for 6 weeks and won't always have access to a cot (even though our little person has pretty much transitioned to a bed but still moves quite a bit in the bed). I am concerned about falling out of bed and onto hard surfaces.

Red Nose has no specific recommendations in relations to a travel mattress.

However, some of Red Nose Cot to bed information may be helpful.

One option is to take the mattress from a cot or a full height single bed and use it made up on the floor. Ensure the mattress is positioned away from the walls as young children can become trapped between the mattress and wall.

A child’s mattress needs to be firm to prevent sleep accidents. Keep the area around the mattress clear of soft toys, bean bags, plastic bags or similar objects that a young child can roll onto. Soft objects could mould around a young child’s face, resulting in suffocation
https://rednose.org.au/article/transitioning-from-a-cot-to-bed

Also remember to look for risks where he is sleeping to ensure his environment is safe from hazards that he may now have access to now he is no longer in a cot.
If using an inflatable mattress, ensure it is firm.
Also have a look at our cot to bed brochure
https://rednose.org.au/downloads/Cot_to_bed_brochure_for_families.pdf

If you are camping (or in caravan) you may find some of this info helpful.
https://rednose.org.au/article/how-to-keep-your-baby-safe-if-youre-camping-this-summer