I'd use H4 - or H3 TP so long as the timber is on concrete or stirrups/ post brackets at the lower end and not on the dirt. Size depends on the span between supports. If you intend having simply a 3200 run and no intermediate supports then you would need to scale up - 190x45 will go 3100mm and might be OK for 3200, but I'd go 240x45 to have no flexing. Or if the soil is OK you could put in a centre bearer of 90x45 (or a bit bigger) between two stirrups and use 90x45 joists.
Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.