For doorway thresholds too high for small robots, often limited to 1.5cm height, rubber ramps made for wheel chair access might be used. Some of these are only 1 in. high, 8 in. deep, and could be cut off at lower heights. Narrower pieces might need to be fastened to the floor with double stick tape etc.
Example at Amazon https://www.amazon.com/MAGIC-UNION-Whee ... r=8-1&th=1
Rather expensive materials for their size, probably reflecting medical market conditions (wheel chairs).
Beveled wood molding is made for window framing, in building supply.
Another material is electrical cord covers for floors, which might be cut in two, but light weight and needs fastening down.