alternative to Gitzo baseplate

I'm looking forward to get a second baseplate ... To swap different heads more quickly.

In that case, rather than swap Gitzo baseplates on the tripod, the better (faster, cheaper) option is to mount a quick-release (QR) clamp on the existing baseplate on your tripod, then mount compatible QR dovetail plates on the heads you want to swap out on your tripod.

Probably the most common platform to this is with the Arca-Swiss–style QR clamp and plate system. There are other styles (such as the Manfrotto system, etc.), but the Arca-Swiss–style is probably the most universal.

Pick a large clamp to mount on your tripod's baseplate, such a 70mm or 80mm clamp. The clamp can be lever-action release, which is very quick to change, or screw-type, which is more universal amongst minor variations in plate dimensions and can always provide the desired clamping force.

A long time ago, I went with a Really Right Stuff Series 3 tripod (roughly equivalent to your Gitzo Series 3) with the appropriate lever base clamp, and all my heads have the necessary matching dovetail plate. Supposedly, RRS lever clamps might not be compatible with certain plates (notably, Novoflex). I have not used Novoflex plates with my clamps, but over the years I have acquired several different clamps and plates. I can attest that my RRS clamps (both lever and screw type), as well as Acratech, Hejnar Photo, and various Chinese-branded clamps like Sunway Foto, all work with my RRS, Acratech, Sunway Foto, and other plates I use.

See also:

• What are pros and cons of different quick release systems?
• How important is quick release for a tripod?
• Can quick release plates be bought separately from ball-head?
• Is the Arca Swiss Z1 compatible with Kirk brackets
• Which tripod heads accept the Arca-Swiss plate system?
• Arca Swiss compatibility questions
• Are L-plates and anti-twist plates only made for the Arca Swiss QR system?
• Are Manfrotto Q6 Plates Compatible with Acratech GP-ss Ball-Heads?